[llvm] [AMDGPU] Remove SIWholeQuadMode pass early exit (PR #98450)

[Jay Foad via llvm-commits]

https://github.com/jayfoad commented:

Seems reasonable but it would be easier to review if you can separate out the refactoring, the bug fix and the optimization.

https://github.com/llvm/llvm-project/pull/98450