[llvm] [NVPTX] Fix the error in a pattern match in v4i8 comparisons. (PR #81308)

[Thomas Raoux via llvm-commits]

https://github.com/ThomasRaoux approved this pull request.

I don't understand all the details of the original bug but the code change looks good to me. Thanks for checking that SASS is not worse for cases where we have more ptx insts!

https://github.com/llvm/llvm-project/pull/81308