You can wash your comforter in a top load washing machine as long as the comforter fits perfectly in the top load washing machine around the agitator.
It's more recommended to wash comforters in front load washing machines though to give the comforter more room without the agitator being in the way.
But as long as you can fit the comforter in the top load washing machine with room to spare and without bunching it up around the agitator then it should be fine.