[Bugfix] Fix value unpack error of simple connector for KVCache transfer. (#11058)

Signed-off-by: ShangmingCai <csmthu@gmail.com>

vllm/distributed/kv_transfer/kv_connector/simple_connector.py

@@ -118,6 +118,12 @@ class SimpleConnector(KVConnectorBase):
         start_layer = model_executable.model.start_layer
         end_layer = model_executable.model.end_layer
 
+        model_config = model_executable.model.config
+        num_heads = model_config.num_key_value_heads
+        hidden_size = model_config.hidden_size
+        num_attention_heads = model_config.num_attention_heads
+        head_size = int(hidden_size / num_attention_heads)
+
         # query_lens contains new KV caches that are added to vLLM.
         # so we will send them to decode instance
         # FIXME(Kuntai): This assume that all requests are prefill.
@@ -131,8 +137,6 @@ class SimpleConnector(KVConnectorBase):
             for layer_id in range(start_layer, end_layer):
                 kv_cache = kv_caches[layer_id - start_layer]
 
-                _, _, num_heads, head_size = kv_cache[0].shape
-
                 key_cache = kv_cache[0].reshape(-1, num_heads, head_size)
                 value_cache = kv_cache[1].reshape(-1, num_heads, head_size)