Turn off media player.

async def turn_off(self):
        """Turn off media player."""
        _LOGGER.debug("turn_off while %s", self._state)
        if self._state in [State.PLAYING_LIVE_TV, State.PLAYING_RECORDED_TV,
                          State.PLAYING_TIMESHIFT_TV, State.UNKNOWN]:
            await self.send_cmd('Power')
            self._state = State.OFF
        return self._state