fix the model evaluation error

Link: https://code.alibaba-inc.com/Ali-MaaS/MaaS-lib/codereview/8872484

maas_lib/trainers/nlp/sequence_classification_trainer.py

@@ -128,7 +128,7 @@ class SequenceClassificationTrainer(BaseTrainer):
             collate_fn=pre_dataset.batch_fn)
 
         # generate a model
-        model = SequenceClassification(checkpoint_path)
+        model = SequenceClassification.from_pretrained(checkpoint_path)
 
         # copy from easynlp (start)
         model.eval()