[AArch64] Fix -Wunused-variable in -DLLVM_ENABLE_ASSERTIONS=off builds after r366857
[AArch64] Fix -Wunused-variable in -DLLVM_ENABLE_ASSERTIONS=off builds after r366857

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@366866 91177308-0d34-0410-b5e6-96231b3b80d8

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