[llvm] [AMDGPU] Fix llvm.amdgcn.ballot with return width != wavefront size (PR #211493)

[Arseniy Obolenskiy via llvm-commits]

aobolensk wrote:

> Weird that this is enforced in selection in gisel, but lowering in sdag

Gonna address in the upcoming patch, thanks!

https://github.com/llvm/llvm-project/pull/211493