[llvm] [AMDGPU] Fix instruction size of LDS-DMA buffer loads (PR #211302)

[Michael Halkenhäuser via llvm-commits]

mhalk wrote:

Thanks for the feedback, I added the unit test and fleshed it out a bit.
Decided to keep the lit test for now, let me know if you'd rather drop it.

https://github.com/llvm/llvm-project/pull/211302