[BugFix] Fix deepseek v3.2 mtp bug. (#3900)

### What this PR does / why we need it?
This PR fixes deepseek v3.2 mtp bug.

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

### How was this patch tested?
All existed ci tests should pass.

- vLLM version: v0.11.0
- vLLM main:
83f478bb19

---------

Signed-off-by: whx-sjtu <2952154980@qq.com>

vllm_ascend/spec_decode/mtp_proposer.py

@@ -13,6 +13,7 @@ from vllm.model_executor.model_loader import get_model_loader
 from vllm.model_executor.model_loader.utils import \
     process_weights_after_loading
 from vllm.model_executor.models.deepseek_mtp import DeepSeekMTP
+from vllm.model_executor.models.deepseek_v2 import DeepseekV32IndexerCache
 from vllm.model_executor.models.llama_eagle3 import Eagle3LlamaForCausalLM
 from vllm.utils import cdiv
 from vllm.v1.attention.backends.utils import (AttentionMetadataBuilder,
@@ -139,6 +140,9 @@ class MtpProposer(Proposer):
         target_attn_layer_names = set(
             get_layers_from_vllm_config(self.vllm_config,
                                         AttentionLayerBase).keys())
+        target_indexer_layer_names = set(
+            get_layers_from_vllm_config(self.vllm_config,
+                                        DeepseekV32IndexerCache).keys())
         draft_model_config = \
             self.vllm_config.speculative_config.draft_model_config
         target_device = self.vllm_config.device_config.device
@@ -152,6 +156,13 @@ class MtpProposer(Proposer):
         draft_attn_layer_names = (get_layers_from_vllm_config(
             self.vllm_config, AttentionLayerBase).keys() -
                                   target_attn_layer_names)
+        indexer_layers = get_layers_from_vllm_config(self.vllm_config,
+                                                     DeepseekV32IndexerCache)
+        draft_indexer_layer_names = indexer_layers.keys(
+        ) - target_indexer_layer_names
+        # NOTE: Currently we don't have specific attention backend and attention metadata
+        # for deepseek v3.2 indexer, so we just exclude the indexer layers here.
+        draft_attn_layer_names = draft_attn_layer_names - draft_indexer_layer_names
 
         assert len(draft_attn_layer_names) == 1
         self.attn_layer_name = list(draft_attn_layer_names)