[llvm] [LoopIdiom] Fix miscompile for big-endian sub-byte CRC (PR #213040)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-nvptx-nvidia-win` running on `as-builder-8` while building `llvm` at step 7 "test-build-unified-tree-check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/54/builds/22000

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

```
Step 7 (test-build-unified-tree-check-llvm) failure: test (failure)
...
Total Discovered Tests: 68961
  Skipped: 68961 (100.00%)

1 error(s) in tests
unittests\ExecutionEngine\MCJIT\MCJITTests.exe
[886/890] Linking CXX executable unittests\Transforms\Scalar\ScalarTests.exe
[887/890] Linking CXX executable unittests\Target\X86\X86Tests.exe
[888/890] Building CXX object unittests\ObjectYAML\CMakeFiles\ObjectYAMLTests.dir\DXContainerYAMLTest.cpp.obj
[889/890] Linking CXX executable unittests\ObjectYAML\ObjectYAMLTests.exe
[889/890] Running the LLVM regression tests
FAILED: test/CMakeFiles/check-llvm C:/buildbot/as-builder-8/llvm-nvptx-nvidia-win/build/test/CMakeFiles/check-llvm 
C:\Windows\system32\cmd.exe /C "cd /D C:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\build\test && C:\Python313\python.exe C:/buildbot/as-builder-8/llvm-nvptx-nvidia-win/build/./bin/llvm-lit.py -vv C:/buildbot/as-builder-8/llvm-nvptx-nvidia-win/build/test"
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/213040