AMDGPU: Swap order of operands in fadd/fsub combine

FMA is canonicalized to constant in the middle operand. Do
the same so fmad matches and avoid an extra combine step.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290313 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed