[Fix] fp16 unscaling in train_dreambooth_lora_sdxl (#10889)

Fix fp16 bug
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>

examples/dreambooth/train_dreambooth_lora_sdxl.py

@@ -203,7 +203,7 @@ def log_validation(
 
         pipeline.scheduler = DPMSolverMultistepScheduler.from_config(pipeline.scheduler.config, **scheduler_args)
 
-    pipeline = pipeline.to(accelerator.device, dtype=torch_dtype)
+    pipeline = pipeline.to(accelerator.device)
     pipeline.set_progress_bar_config(disable=True)
 
     # run inference
@@ -213,7 +213,7 @@ def log_validation(
     if torch.backends.mps.is_available() or "playground" in args.pretrained_model_name_or_path:
         autocast_ctx = nullcontext()
     else:
-        autocast_ctx = torch.autocast(accelerator.device.type)
+        autocast_ctx = torch.autocast(accelerator.device.type) if not is_final_validation else nullcontext()
 
     with autocast_ctx:
         images = [pipeline(**pipeline_args, generator=generator).images[0] for _ in range(args.num_validation_images)]