[Transformer] fix ORPO loss for MOE models (#479)

## Summary
Add missing MOE loss when specified in the trainer.

- Hardware Type: <BLANK>
- [x] run `make test` to ensure correctness
- [x] run `make checkstyle` to ensure code style
- [x] run `make test-convergence` to ensure convergence

src/liger_kernel/transformers/trainer/orpo_trainer.py

@@ -125,6 +125,10 @@ def orpo_partial(lm_head, last_hidden_state, concatenated_labels):
             outputs.last_hidden_state,
             concatenated_batch["concatenated_labels"],
         )
+        # if aux_loss_enabled, add the aux_loss to the orpo_loss
+        if self.aux_loss_enabled:
+            orpo_loss += self.aux_loss_coef * outputs.aux_loss
+
         return orpo_loss, aux_outputs
 
     def get_batch_loss_metrics(