[Bugfix]fix ep clear buffer perf (#4389)

* fix

* Update fused_moe_backend_base.py

Author: gzy19990617

fastdeploy/model_executor/layers/moe/fused_moe_backend_base.py

@@ -168,12 +168,12 @@ def apply(
         Paddle Cutlass compute Fused MoE.
         """
         if layer.ep_size > 1:
-            if layer.fd_config.model_config.moe_phase.phase == "prefill":
+            if layer.fd_config.model_config.moe_phase.phase == "prefill" and layer.layer_idx == 0:
                 if layer.fd_config.scheduler_config.splitwise_role == "mixed":
                     self.ep_prefill_runner.clean_low_latency_buffer()
                 return self.apply_ep_prefill(layer, x, gate)
             else:
-                if layer.fd_config.scheduler_config.splitwise_role == "mixed":
+                if layer.fd_config.scheduler_config.splitwise_role == "mixed" and layer.layer_idx == 0:
                     self.ep_decoder_runner.clean_low_latency_buffer()
                 return self.apply_ep_decode(layer, x, gate)
         else: