[llvm] Fix parentheses for clarity in X86ISelLowering.cpp (PR #121954)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@soumyaGhoshh Were you successful in getting a working build? The patch LGTM so we can proceed with the merge, but if you're hoping to contribute again in the future you will need to get over these initial stages.

https://github.com/llvm/llvm-project/pull/121954