fix with_argmax for mmseg (#2056)

Author: RunningLeon

mmdeploy/codebase/mmseg/deploy/segmentation.py

@@ -303,10 +303,10 @@ def get_postprocess(self, *args, **kwargs) -> Dict:
         params = self.model_cfg.model.decode_head
         if isinstance(params, list):
             params = params[-1]
-        postprocess = dict(params=params, type='ResizeMask')
         with_argmax = get_codebase_config(self.deploy_cfg).get(
             'with_argmax', True)
-        postprocess['with_argmax'] = with_argmax
+        params['with_argmax'] = with_argmax
+        postprocess = dict(params=params, type='ResizeMask')
         return postprocess
 
     def get_model_name(self, *args, **kwargs) -> str: