[llvm] [AMDGPU] Fix LDS access via flat pointer argument in amdgpu-sw-lower-lds (PR #209842)

[via llvm-commits]

skc7 wrote:

PR is still in draft stage and wanted to quickly test with these changes and check if the issue with rocPRIM (ROCM-24185) could be fixed. Will post the full workaround and instrumentation changes asap.

https://github.com/llvm/llvm-project/pull/209842