[ c10d ] modify API to get device string from device with torch.device (pytorch#146290)

Modify the ```get_default_backend_for_device()``` API to extract the device string using ```torch.device()```

Pull Request resolved: pytorch#146290
Approved by: https://github.com/guangyey, https://github.com/H-Huang

Author: ankurneog

torch/distributed/distributed_c10d.py

@@ -1382,7 +1382,7 @@ def get_default_backend_for_device(device: Union[str, torch.device]) -> str:
     if isinstance(device, torch.device):
         device_str = device.type
     else:
-        device_str = device.split(":")[0]
+        device_str = torch.device(device).type
 
     backend = Backend.default_device_backend_map.get(device_str)
     if backend is None: