[clang] [Clang] Remove 't' from __builtin_amdgcn_flat_atomic_fadd_f32/f64 (PR #173381)

[Juan Manuel Martinez Caamaño via cfe-commits]

jmmartinez wrote:

> Can you add a hip codegen test for these

I've added some in the last commit.

https://github.com/llvm/llvm-project/pull/173381