[llvm] [AMDGPU] Fix lowering of abs for i16 vectors with more than 2 elements (PR #95413)

[Nico Weber via llvm-commits]

nico wrote:

Looks like this breaks tests: http://45.33.8.238/linux/140660/step_11.txt

Please take a look and revert for now if it takes a while to fix.

https://github.com/llvm/llvm-project/pull/95413