[Bugfix] dtype mismatch in ngram gpu propose (#37246)

Signed-off-by: PatchouliTaisa <patchychen@tencent.com>
Co-authored-by: PatchouliTaisa <patchychen@tencent.com>

vllm/v1/spec_decode/ngram_proposer_gpu.py

@@ -364,7 +364,9 @@ class NgramProposerGPU:
         )
         token_ids_gpu.scatter_(1, write_positions_long, tokens_to_scatter)
 
-        num_tokens_tmp = num_tokens_no_spec + valid_sampled_tokens_count
+        num_tokens_tmp = (num_tokens_no_spec + valid_sampled_tokens_count).to(
+            torch.int32
+        )
 
         # Compute validity masks.
         sampled_flags = valid_sampled_tokens_count > 0
@@ -437,7 +439,7 @@ class NgramProposerGPU:
         )
 
         # Count valid tokens per request.
-        valid_sampled_tokens_count = valid_mask.sum(dim=1)
+        valid_sampled_tokens_count = valid_mask.sum(dim=1).to(torch.int32)
 
         # Rightmost valid index per row.
         last_valid_indices = valid_sampled_tokens_count - 1