[llvm] [AMDGPU] Improve MIR pattern for FMinFMaxLegacy combine. NFC. (PR #90968)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

You could hoist:
```
 if ((Info.LHS != True || Info.RHS != False) &&
      (Info.LHS != False || Info.RHS != True))
    return false;
```
into the pattern, but then you to write the pattern twice.

https://github.com/llvm/llvm-project/pull/90968