[llvm] [AMDGPU] fmuladd.f32.ll - clean up prefixes and regenerate checks (PR #151832)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> This test could use more modernization to the content too 

All the fmuladd tests are now auto-generated so adding additional tests should now be a doddle.

https://github.com/llvm/llvm-project/pull/151832