fix mla attention backend (#3176)

Author: gongshaotian

fastdeploy/model_executor/models/deepseek_v3.py

@@ -315,7 +315,7 @@ def forward(
             dtype=layernorm_out.dtype,
         )
 
-        if forward_meta.max_enc_len_this_time:
+        if forward_meta.max_len_tensor_cpu[1]:  # max_enc_len_this_time
             query = self.q_a_proj(layernorm_out)
             query = self.q_a_layernorm(query)
             query = self.q_b_proj(query)
@@ -362,7 +362,7 @@ def forward(
             fmha_out_prefill = fmha_out_prefill * mask_encoder_batch.cast(fmha_out_prefill.dtype)
 
             fmha_out = fmha_out + fmha_out_prefill
-        if forward_meta.max_dec_len_this_time:
+        if forward_meta.max_len_tensor_cpu[2]:  # max_dec_len_this_time
             query = self.q_a_proj(layernorm_out)
             query = self.q_a_layernorm(query)
             ln_out_or_q_c = query