AMDGPU: Fix not checking for copy when looking at copy src
AMDGPU: Fix not checking for copy when looking at copy src

Effectively reverts r356956. The check for isFullCopy was excessive,
but there still needs to be a check that this is a copy.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@358890 91177308-0d34-0410-b5e6-96231b3b80d8

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