Bugfix: wrongly assign gen_config with True (#1594)

* Bugfix: fix bugs with error info:"
 if gen_config.stop_words is None:

AttributeError: 'bool' object has no attribute 'stop_words'",which is caused by assign gen_config with value 'True'.

* Style: Fix flake8 line length issue

lmdeploy/serve/qos_engine/qos_engine.py

@@ -79,7 +79,7 @@ async def generate(self, request):
                 result_generator = self.engine.generate(
                     request.prompt[i],
                     request.session_id + i,
-                    True,  # always use stream to enable batching
+                    stream_response=True,  # always use stream for batching
                     sequence_start=True,
                     sequence_end=True,
                     request_output_len=request.max_tokens
@@ -119,7 +119,7 @@ async def generate(self, request):
             result_generator = self.engine.generate(
                 request.messages,
                 request.session_id,
-                True,  # always use stream to enable batching
+                stream_response=True,  # always use stream to enable batching
                 sequence_start=True,
                 sequence_end=True,
                 request_output_len=request.max_tokens