Fix `mps.empty_cache()` for macOS without MPS (#16280)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/engine/trainer.py

@@ -454,7 +454,7 @@ class BaseTrainer:
                 self.stop |= epoch >= self.epochs  # stop if exceeded epochs
             self.run_callbacks("on_fit_epoch_end")
             gc.collect()
-            if MACOS:
+            if MACOS and self.device.type == "mps":
                 torch.mps.empty_cache()  # clear unified memory at end of epoch, may help MPS' management of 'unlimited' virtual memoy
             else:
                 torch.cuda.empty_cache()  # clear GPU memory at end of epoch, may help reduce CUDA out of memory errors
@@ -479,7 +479,7 @@ class BaseTrainer:
                 self.plot_metrics()
             self.run_callbacks("on_train_end")
         gc.collect()
-        if MACOS:
+        if MACOS and self.device.type == "mps":
             torch.mps.empty_cache()
         else:
             torch.cuda.empty_cache()