AMDGPU/SI: Fix inst-select-load-smrd.mir on some builds

Summary:
For some reason instructions are being inserted in the wrong order with some
builds.  I'm not sure why this is happening.

Reviewers: arsenm

Subscribers: kzhuravl, wdng, nhaehnle, yaxunl, tony-tye, tpr, llvm-commits

Differential Revision: https://reviews.llvm.org/D29325

llvm-svn: 293639