[ROCm] Remove unnecessary fp8 roundtrip in gather cache NHD dequant (#39122)

Signed-off-by: Bortlesboat <bortstheboat@gmail.com>

vllm/v1/attention/backends/rocm_aiter_fa.py

@@ -112,10 +112,12 @@ if current_platform.is_rocm():
             if DEQUANT:
                 k_scale = tl.load(k_scale_ptr)
                 v_scale = tl.load(v_scale_ptr)
-                k_dtype = k_reg.dtype
-                v_dtype = v_reg.dtype
-                k_reg = (k_reg.to(tl.float32) * k_scale).to(k_dtype)
-                v_reg = (v_reg.to(tl.float32) * v_scale).to(v_dtype)
+                k_reg = (k_reg.to(tl.float32) * k_scale).to(
+                    key_ptr_offset.dtype.element_ty
+                )
+                v_reg = (v_reg.to(tl.float32) * v_scale).to(
+                    value_ptr_offset.dtype.element_ty
+                )
             tl.store(key_ptr_offset + col_offsets, k_reg)
             tl.store(value_ptr_offset + col_offsets, v_reg)