[llvm] AMDGPU: Fix incorrectly selecting fp8/bf8 conversion intrinsics (PR #107291)

[Krzysztof Drewniak via llvm-commits]

https://github.com/krzysz00 commented:

Seems fine to me but I can't review this in because I don't know the hardware context to be assured this is correct

https://github.com/llvm/llvm-project/pull/107291