Fix MPS cache cleanup

Importing torch does not import torch.mps so the call failed.

modules/devices.py

@@ -54,8 +54,9 @@ def torch_gc():
         with torch.cuda.device(get_cuda_device_string()):
             torch.cuda.empty_cache()
             torch.cuda.ipc_collect()
-    elif has_mps() and hasattr(torch.mps, 'empty_cache'):
-        torch.mps.empty_cache()
+
+    if has_mps():
+        mac_specific.torch_mps_gc()
 
 
 def enable_tf32():