[Bugfix] Fix ubatch wrapper num_tokens calculate (#33694)

Signed-off-by: jiangkuaixue123 <jiangxiaozhou111@163.com>

vllm/v1/worker/gpu_ubatch_wrapper.py

@@ -412,9 +412,7 @@ class UBatchWrapper:
 
         attn_metadata = forward_context.attn_metadata
         slot_mapping = forward_context.slot_mapping
-        num_tokens = (
-            ubatch_slices[0].token_slice.stop - ubatch_slices[0].token_slice.start
-        ) * 2
+        num_tokens = sum(ubatch_slice.num_tokens for ubatch_slice in ubatch_slices)
         input_ids = kwargs["input_ids"]
         positions = kwargs["positions"]
         intermediate_tensors = kwargs["intermediate_tensors"]