message: Fix return result in backend base class run_model
diff: @@ -54,7 +54,7 @@ class Backend(object):
  @classmethod
  def run_model(cls, model, inputs, device='CPU', **kwargs):
  - cls.prepare(model, device, **kwargs).run(inputs)
  + return cls.prepare(model, device, **kwargs).run(inputs)
  @classmethod
  def run_node(cls, node, inputs, device='CPU'):
  