[Bugfix] Fix FP8 torch._scaled_mm fallback for torch>2.5 with CUDA<12.4 (#10095)

Signed-off-by: mgoin <michael@neuralmagic.com>

vllm/model_executor/layers/quantization/utils/w8a8_utils.py

@@ -7,8 +7,7 @@ from vllm.platforms import current_platform
 
 # Input scaling factors are no longer optional in _scaled_mm starting
 # from pytorch 2.5. Allocating a dummy tensor to pass as input_scale
-TORCH_DEVICE_IDENTITY = torch.ones(1).cuda() \
-            if current_platform.is_rocm() else None
+TORCH_DEVICE_IDENTITY = torch.ones(1, dtype=torch.float32)
 
 
 def cutlass_fp8_supported() -> bool:
@@ -166,8 +165,7 @@ def apply_fp8_linear(
 
             # Making sure the dummy tensor is on the same device as the weight
             global TORCH_DEVICE_IDENTITY
-            if (TORCH_DEVICE_IDENTITY is not None
-                    and TORCH_DEVICE_IDENTITY.device != weight.device):
+            if TORCH_DEVICE_IDENTITY.device != weight.device:
                 TORCH_DEVICE_IDENTITY = TORCH_DEVICE_IDENTITY.to(weight.device)
 
             # GEMM