[clang] AMDGPU: Find device files even when ROCM_PATH is set (PR #177346)

[Shilei Tian via cfe-commits]

shiltian wrote:

> This PR's behavior is confusing to me because it seems to defy what `ROCM_PATH` is intended to do, which is to override the search path, into just a "suggestion".

That's exactly the reason I think this PR has fundamental issue.

https://github.com/llvm/llvm-project/pull/177346