[llvm] [AMDGPU] Use const with MI in AMDGPULowerVGPREncoding::computeMode. NFC (PR #181900)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-aarch64-windows` running on `linaro-armv8-windows-msvc-05` while building `llvm` at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/141/builds/15532

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test) failure: build (failure)
...
XFAIL: lldb-api :: functionalities/scripted_frame_provider/circular_dependency/TestFrameProviderCircularDependency.py (621 of 2449)
UNSUPPORTED: lldb-api :: functionalities/scripted_process/TestScriptedProcess.py (622 of 2449)
UNSUPPORTED: lldb-api :: functionalities/scripted_process/TestStackCoreScriptedProcess.py (623 of 2449)
UNSUPPORTED: lldb-api :: functionalities/scripted_process_empty_memory_region/TestScriptedProcessEmptyMemoryRegion.py (624 of 2449)
UNSUPPORTED: lldb-api :: functionalities/set-data/TestSetData.py (625 of 2449)
PASS: lldb-api :: functionalities/show_location/TestShowLocationDwarf5.py (626 of 2449)
UNSUPPORTED: lldb-api :: functionalities/signal/TestSendSignal.py (627 of 2449)
UNSUPPORTED: lldb-api :: functionalities/signal/handle-abrt/TestHandleAbort.py (628 of 2449)
UNSUPPORTED: lldb-api :: functionalities/signal/handle-segv/TestHandleSegv.py (629 of 2449)
UNSUPPORTED: lldb-api :: functionalities/signal/raise/TestRaise.py (630 of 2449)
FAIL: lldb-api :: functionalities/reverse-execution/TestReverseContinueBreakpoints.py (631 of 2449)
******************** TEST 'lldb-api :: functionalities/reverse-execution/TestReverseContinueBreakpoints.py' FAILED ********************
Script:
--
C:/Users/tcwg/scoop/apps/python/current/python.exe C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/llvm-project/lldb\test\API\dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./lib --env LLVM_INCLUDE_DIR=C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/include --env LLVM_TOOLS_DIR=C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin --arch aarch64 --build-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/lldb-test-build.noindex --lldb-module-cache-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/lldb-test-build.noindex/module-cache-lldb\lldb-api --clang-module-cache-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/lldb-test-build.noindex/module-cache-clang\lldb-api --executable C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin/lldb.exe --compiler C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin/clang.exe --dsymutil C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin/dsymutil.exe --make C:/Users/tcwg/scoop/shims/make.exe --llvm-tools-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./bin --lldb-obj-root C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/tools/lldb --lldb-libs-dir C:/Users/tcwg/llvm-worker/lldb-aarch64-windows/build/./lib --cmake-build-type Release --skip-category=watchpoint C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\test\API\functionalities\reverse-execution -p TestReverseContinueBreakpoints.py
--
Exit Code: 1

Command Output (stdout):
--
lldb version 23.0.0git (https://github.com/llvm/llvm-project.git revision 537e09b70d17d89bfcabbcb67994e613c911bcee)
  clang revision 537e09b70d17d89bfcabbcb67994e613c911bcee
  llvm revision 537e09b70d17d89bfcabbcb67994e613c911bcee
Skipping the following test categories: watchpoint, libc++, libstdcxx, dwo, dsym, gmodules, debugserver, objc, fork, pexpect

An exception happened when receiving the response from the gdb server. Closing the client...


--
Command Output (stderr):
--
Traceback (most recent call last):

  File "C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\packages\Python\lldbsuite\test\gdbclientutils.py", line 606, in run

    self._receive(data)

  File "C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\packages\Python\lldbsuite\test\gdbclientutils.py", line 626, in _receive

    self._handlePacket(packet)

  File "C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\packages\Python\lldbsuite\test\gdbclientutils.py", line 719, in _handlePacket

    response = self.responder.respond(packet)

               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\packages\Python\lldbsuite\test\lldbreverse.py", line 116, in respond


```

</details>

https://github.com/llvm/llvm-project/pull/181900