[AMDGPU] Fix bug introduced in 47a5c36b

Summary: [AMDGPU] Fix bug introduced in 47a5c36b

Reviewers: foad, arsenm

Reviewed By: arsenm

Subscribers: arsenm, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69915