[llvm] [LoongArch] Fix xvshuf instructions lowering (PR #145868)

[Lu Weining via llvm-commits]

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

LGTM. This is a bug since llvm-19. And I hope it can be cherry-picked to llvm-20 if possible.

https://github.com/llvm/llvm-project/pull/145868