AMDGPU: Fix SMRD test in trivially disjoint mem access code

Summary:
This seems like an obvious error - cut and paste issue?
The change does make a change to one of the lit tests - it stops s_buffer_load
re-ordering past an MUBUF instruction (which is not surprising).

Change-Id: I80be99de5b62af4f42e91af2591b76a52ac9efa6

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D75686