Fix EMA in train_text_to_image_sdxl.py (huggingface#7048)

* Fix typos

examples/text_to_image/train_text_to_image_sdxl.py

@@ -951,6 +951,9 @@ def collate_fn(examples):
         unet, optimizer, train_dataloader, lr_scheduler
     )
 
+    if args.use_ema:
+        ema_unet.to(accelerator.device)
+
     # We need to recalculate our total training steps as the size of the training dataloader may have changed.
     num_update_steps_per_epoch = math.ceil(len(train_dataloader) / args.gradient_accumulation_steps)
     if overrode_max_train_steps:
@@ -1126,6 +1129,8 @@ def compute_time_ids(original_size, crops_coords_top_left):
 
             # Checks if the accelerator has performed an optimization step behind the scenes
             if accelerator.sync_gradients:
+                if args.use_ema:
+                    ema_unet.step(unet.parameters())
                 progress_bar.update(1)
                 global_step += 1
                 accelerator.log({"train_loss": train_loss}, step=global_step)