[media] mt9m032: use the available subdev pointer, don't re-calculate it

	struct v4l2_subdev *subdev = i2c_get_clientdata(client);

	struct mt9m032 *sensor = to_mt9m032(subdev);

	v4l2_device_unregister_subdev(&sensor->subdev);

	v4l2_device_unregister_subdev(subdev);

	v4l2_ctrl_handler_free(&sensor->ctrls);

	media_entity_cleanup(&sensor->subdev.entity);

	media_entity_cleanup(&subdev->entity);

	mutex_destroy(&sensor->lock);

	kfree(sensor);

	return 0;