[Op] Canonicalize SaveV2 Op device spec in distributed training. (#925)

Signed-off-by: 泊霆 <hujunqi.hjq@alibaba-inc.com>

tensorflow/python/training/saver.py

@@ -550,8 +550,12 @@ def _GroupByDevices(self, saveables):
     """
     per_device = collections.defaultdict(lambda: [])
     for saveable in saveables:
-      canonical_device = set(
-          pydev.canonical_name(spec.tensor.device) for spec in saveable.specs)
+      canonical_device = set()
+      for spec in saveable.specs:
+        device_name = pydev.canonical_name(spec.tensor.device)
+        device_spec = pydev.DeviceSpec.from_string(device_name)
+        device_spec.device_type = "CPU"
+        canonical_device.add(device_spec.to_string())
       if len(canonical_device) != 1:
         raise ValueError("All tensors of a saveable object must be "
                          "on the same device: %s" % saveable.name)