fix cli serve --help (#3895)

Author: RunningLeon

lmdeploy/cli/utils.py

@@ -572,7 +572,7 @@ def enable_eplb(parser):
     @staticmethod
     def enable_metrics(parser):
         """Add argument enable_metrics to parser."""
-        parser.add_argument('--enable-metrics', action='store_true', default=False, help='enable metrics system')
+        return parser.add_argument('--enable-metrics', action='store_true', default=False, help='enable metrics system')
 
     # For Disaggregation
     @staticmethod
@@ -596,19 +596,19 @@ def migration_backend(parser):
     @staticmethod
     def disable_vision_encoder(parser):
         """Disable loading vision encoder."""
-        parser.add_argument('--disable-vision-encoder',
-                            action='store_true',
-                            default=False,
-                            help='enable metrics system')
+        return parser.add_argument('--disable-vision-encoder',
+                                   action='store_true',
+                                   default=False,
+                                   help='enable metrics system')
 
     @staticmethod
     def logprobs_mode(parser):
         """The mode of logprobs."""
-        parser.add_argument('--logprobs-mode',
-                            type=str,
-                            default=None,
-                            choices=[None, 'raw_logits', 'raw_logprobs'],
-                            help='The mode of logprobs.')
+        return parser.add_argument('--logprobs-mode',
+                                   type=str,
+                                   default=None,
+                                   choices=[None, 'raw_logits', 'raw_logprobs'],
+                                   help='The mode of logprobs.')
 
 
 # adapted from https://github.com/vllm-project/vllm/blob/main/vllm/utils/__init__.py