[AMDGPU] Fix DPP operand order in atomic optimizer.
[AMDGPU] Fix DPP operand order in atomic optimizer.

Ensure order of operands in DPP atomic optimizer final WWM step
is appropriate for sub instructions.

Change-Id: I631d050e1c00a3b4bc7c11a90437064403c4cf30

GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm