[utils] account for MPS when available in get_device(). (#11905)

* account for MPS when available in get_device().

* fix

src/diffusers/utils/torch_utils.py

@@ -175,6 +175,8 @@ def get_device():
         return "npu"
     elif hasattr(torch, "xpu") and torch.xpu.is_available():
         return "xpu"
+    elif torch.backends.mps.is_available():
+        return "mps"
     else:
         return "cpu"