[llvm] [SelectionDAG] Simplify classof of MemSDNode and MemIntrinsicSDNode (NFC) (PR #115720)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `libc-x86_64-debian` running on `libc-x86_64-debian` while building `llvm` at step 4 "annotate".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/43/builds/10080

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

```
Step 4 (annotate) failure: 'python ../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py ...' (failure)
...
[       OK ] LlvmLibcFStatTest.NonExistentFile (4 us)
Ran 2 tests.  PASS: 2  FAIL: 0
[922/984] Running unit test libc.test.src.sys.statvfs.linux.statvfs_test
[==========] Running 2 tests from 1 test suite.
[ RUN      ] LlvmLibcSysStatvfsTest.StatvfsBasic
[       OK ] LlvmLibcSysStatvfsTest.StatvfsBasic (15 us)
[ RUN      ] LlvmLibcSysStatvfsTest.StatvfsInvalidPath
[       OK ] LlvmLibcSysStatvfsTest.StatvfsInvalidPath (136 us)
Ran 2 tests.  PASS: 2  FAIL: 0
[923/984] Running unit test libc.test.src.sys.statvfs.linux.fstatvfs_test
FAILED: projects/libc/test/src/sys/statvfs/linux/CMakeFiles/libc.test.src.sys.statvfs.linux.fstatvfs_test /home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian/libc-x86_64-debian/build/projects/libc/test/src/sys/statvfs/linux/CMakeFiles/libc.test.src.sys.statvfs.linux.fstatvfs_test 
cd /home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian/libc-x86_64-debian/build/projects/libc/test/src/sys/statvfs/linux && /home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian/libc-x86_64-debian/build/projects/libc/test/src/sys/statvfs/linux/libc.test.src.sys.statvfs.linux.fstatvfs_test.__build__
[==========] Running 2 tests from 1 test suite.
[ RUN      ] LlvmLibcSysFStatvfsTest.FStatvfsBasic
[       OK ] LlvmLibcSysFStatvfsTest.FStatvfsBasic (20 us)
[ RUN      ] LlvmLibcSysFStatvfsTest.FStatvfsInvalidPath
/home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian/libc-x86_64-debian/llvm-project/libc/test/src/sys/statvfs/linux/fstatvfs_test.cpp:40: FAILURE
Failed to match LIBC_NAMESPACE::mkdirat(AT_FDCWD, TEST_DIR, S_IRWXU) against Succeeds(0).
Expected return value to be equal to 0 but got -1.
Expected errno to be equal to "Success" but got "File exists".
[  FAILED  ] LlvmLibcSysFStatvfsTest.FStatvfsInvalidPath
Ran 2 tests.  PASS: 1  FAIL: 1
[924/984] Running unit test libc.test.src.sys.utsname.uname_test
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcUnameTest.GetMachineName
[       OK ] LlvmLibcUnameTest.GetMachineName (6 us)
Ran 1 tests.  PASS: 1  FAIL: 0
[925/984] Running unit test libc.test.src.sys.wait.waitpid_test
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcWaitPidTest.NoHangTest
[       OK ] LlvmLibcWaitPidTest.NoHangTest (4 us)
Ran 1 tests.  PASS: 1  FAIL: 0
[926/984] Running unit test libc.test.src.sys.wait.wait4_test
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcwait4Test.NoHangTest
[       OK ] LlvmLibcwait4Test.NoHangTest (5 us)
Ran 1 tests.  PASS: 1  FAIL: 0
[927/984] Running unit test libc.test.src.string.memmove_opt_host_test.__unit__
[==========] Running 7 tests from 1 test suite.
[ RUN      ] LlvmLibcMemmoveTest.MoveZeroByte
[       OK ] LlvmLibcMemmoveTest.MoveZeroByte (3 us)
[ RUN      ] LlvmLibcMemmoveTest.DstAndSrcPointToSameAddress
[       OK ] LlvmLibcMemmoveTest.DstAndSrcPointToSameAddress (1 us)
[ RUN      ] LlvmLibcMemmoveTest.DstStartsBeforeSrc
[       OK ] LlvmLibcMemmoveTest.DstStartsBeforeSrc (1 us)
[ RUN      ] LlvmLibcMemmoveTest.DstStartsAfterSrc
[       OK ] LlvmLibcMemmoveTest.DstStartsAfterSrc (2 us)
[ RUN      ] LlvmLibcMemmoveTest.SrcFollowDst
[       OK ] LlvmLibcMemmoveTest.SrcFollowDst (1 us)

```

</details>

https://github.com/llvm/llvm-project/pull/115720