[Fix] Resolve data-parallel (DP) assertion errors in TorchAir (#2626)

### What this PR does / why we need it?
It is confirmed that `num_input_tokens` must be assigned the value of
`maybe_padded_num_tokens` under all circumstances.

### Does this PR introduce _any_ user-facing change?
None.

### How was this patch tested?
Waiting for daily test for TorchAir.
- vLLM version: v0.10.1.1
- vLLM main:
006477e60b

Signed-off-by: Yizhou Liu <liu_yizhou@outlook.com>

vllm_ascend/torchair/torchair_model_runner.py

@@ -100,7 +100,7 @@ class NPUTorchairModelRunner(NPUModelRunner):
             num_tokens_across_dp = torch.full((self.dp_size, ),
                                               maybe_padded_num_tokens,
                                               dtype=torch.int32,
-                                              device="cpu")
+                                              device="npu")
         else:
             maybe_padded_num_tokens = num_tokens