Cast ev initial value

Signed-off-by: Lyaction <guocfly@gmail.com>

tensorflow/python/ops/kv_variable_ops.py

@@ -740,7 +740,7 @@ def sparse_read(self, indices, name=None, ev_init_value=None, counts=None):
       if self._trainable:
         tape.variable_accessed(self)
       if ev_init_value is not None:
-        default_value = ev_init_value
+        default_value = math_ops.cast(ev_init_value, self.dtype)
         is_use_default_value_tensor = True
       else:
         default_value = ops.convert_to_tensor(1.0, dtype=self.dtype)