[BugFix][ROCm] Fix `get_cu_count` missing variable error (#28608)

Signed-off-by: ganyi <ygan@amd.com>

vllm/utils/platform_utils.py

@@ -24,7 +24,7 @@ def xpu_is_initialized() -> bool:
     return torch.xpu.is_initialized()
 
 
-def get_cu_count(cls, device_id: int = 0) -> int:
+def get_cu_count(device_id: int = 0) -> int:
     """Returns the total number of compute units (CU) on single GPU."""
     return torch.cuda.get_device_properties(device_id).multi_processor_count