AMDGPU: Fix alignments in test

I don't think this test was intending to test unaligned load/store.
Change it to use the natural alignment to avoid regressing.

Also adds missing SI checks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261571 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed