fix rlhf callback

Former-commit-id: f5485452d660caef56474cb7dc37abbe4f34599e

src/llmtuner/train/ppo/trainer.py

@@ -45,6 +45,7 @@ class CustomPPOTrainer(PPOTrainer, Trainer):
         self.args = training_args
         self.model_args = model_args
         self.finetuning_args = finetuning_args
+        self.reward_model = reward_model
 
         self.generation_config = GenerationConfig(
             pad_token_id=self.tokenizer.pad_token_id,
@@ -72,8 +73,6 @@ class CustomPPOTrainer(PPOTrainer, Trainer):
                     self.reward_model = self._prepare_deepspeed(self.reward_model)
             else:
                 self.reward_model = self.accelerator.prepare_model(self.reward_model, evaluation_mode=True)
-        else:
-            self.reward_model = None
 
     def ppo_train(self) -> None:
         r"""