[llvm] [AMDGPU] Eliminate redundant s_round_mode and s_denorm_mode writes (PR #216305)

[Barbara Mitic via llvm-commits]

barbara-amd wrote:

Updated according to the latest review: inlined the two mode-write cases, kept the early-exit guard with a comment that it has no functional effect, removed the redundant isCall check and kept isInlineAsm.

https://github.com/llvm/llvm-project/pull/216305