feat: add mtp ut and fix some bugs (#2453)

### What this PR does / why we need it?
Fix mtp mode ut

### Does this PR introduce _any_ user-facing change?
Nothing

### How was this patch tested?
This can be tested in the same way as a unit test.


- vLLM version: v0.10.0
- vLLM main:
53415653ff

Signed-off-by: 赵江江 <zhaojiangjiang1@h-partners.com>
Co-authored-by: 赵江江 <zhaojiangjiang1@h-partners.com>

vllm_ascend/models/deepseek_mtp.py

@@ -215,4 +215,4 @@ class CustomDeepSeekMTP(DeepSeekMTP):
         hidden_states = self.model(input_ids, positions, kv_caches,
                                    attn_metadata, previous_hidden_states,
                                    inputs_embeds, spec_step_idx)
-        return hidden_states
+        return hidden_states