[llvm] [LoongArch] Simplily fix extractelement on LA32 (PR #159564)

[via llvm-commits]

zhaoqi5 wrote:

> Thanks for fixing LA32. There’s an ongoing branch working on fixing the LA32 vector. Since the work isn’t complete yet, no PR has been opened. In the meantime, feel free to submit separate PRs for individual test issues that are blocking progress.
> 
> https://github.com/heiher/llvm-project/commits/la32-vec

I am doing some optimization and want to add tests for la32 at meantime, but errors occured. So I push this simply fix firstly.

Vectorization on la32 indeed still need many fixes. Thanks for your continuous works on it.

https://github.com/llvm/llvm-project/pull/159564