fix(rocm): add early return in get_flash_attn_version for ROCm (#31286)

Signed-off-by: rabi <ramishra@redhat.com>

vllm/attention/utils/fa_utils.py

@@ -40,6 +40,9 @@ def get_flash_attn_version(requires_alibi: bool = False) -> int | None:
 
     if current_platform.is_xpu():
         return 2
+    if current_platform.is_rocm():
+        # ROCm doesn't use vllm_flash_attn; return None to skip fa_version arg
+        return None
     try:
         from vllm.vllm_flash_attn.flash_attn_interface import (
             fa_version_unsupported_reason,