[docs] fix outdated example code in trainer.md (#36066)

fix bugs

docs/source/en/trainer.md

@@ -130,7 +130,7 @@ from torch import nn
 from transformers import Trainer
 
 class CustomTrainer(Trainer):
-    def compute_loss(self, model, inputs, return_outputs=False):
+    def compute_loss(self, model, inputs, return_outputs=False, num_items_in_batch=None):
         labels = inputs.pop("labels")
         # forward pass
         outputs = model(**inputs)
@@ -156,9 +156,7 @@ class EarlyStoppingCallback(TrainerCallback):
 
     def on_step_end(self, args, state, control, **kwargs):
         if state.global_step >= self.num_steps:
-            return {"should_training_stop": True}
-        else:
-            return {}
+            control.should_training_stop = True
 ```
 
 Then pass it to the [`Trainer`]'s `callback` parameter.
@@ -737,7 +735,7 @@ accelerate launch --num_processes=2 \
     --fsdp_transformer_layer_cls_to_wrap="BertLayer" \
     --fsdp_sharding_strategy=1 \
     --fsdp_state_dict_type=FULL_STATE_DICT \
-    ./examples/pytorch/text-classification/run_glue.py
+    ./examples/pytorch/text-classification/run_glue.py \
     --model_name_or_path google-bert/bert-base-cased \
     --task_name $TASK_NAME \
     --do_train \