[llvm] [SelectionDAG] Remove single quote around GET_ROUNDING in doxygen comment in ISDOPcode.h. NFC (PR #172114)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-mlir-rhel-clang` running on `ppc64le-mlir-rhel-test` while building `llvm` at step 6 "test-build-check-mlir-build-only-check-mlir".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/129/builds/34948

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

```
Step 6 (test-build-check-mlir-build-only-check-mlir) failure: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
...
PASS: MLIR-Unit :: IR/./MLIRIRTests/100/131 (3748 of 3760)
PASS: MLIR-Unit :: IR/./MLIRIRTests/101/131 (3749 of 3760)
PASS: MLIR :: mlir-tblgen/llvm-intrinsics.td (3750 of 3760)
PASS: MLIR-Unit :: IR/./MLIRIRTests/0/131 (3751 of 3760)
PASS: MLIR-Unit :: IR/./MLIRIRTests/39/131 (3752 of 3760)
PASS: MLIR-Unit :: Interfaces/./MLIRInterfacesTests/12/22 (3753 of 3760)
PASS: MLIR-Unit :: Pass/./MLIRPassTests/11/14 (3754 of 3760)
PASS: MLIR-Unit :: IR/./MLIRIRTests/38/131 (3755 of 3760)
PASS: MLIR-Unit :: Interfaces/./MLIRInterfacesTests/13/22 (3756 of 3760)
PASS: MLIR-Unit :: Interfaces/./MLIRInterfacesTests/11/22 (3757 of 3760)
command timed out: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2488.498467

```

</details>

https://github.com/llvm/llvm-project/pull/172114