There are multiple ways of answering this question.

1. Ravana did Bhakti. He also did something else - bad deeds. So he got what he paid for. But still he attained moksha by being killed in the hands of God. What more could he have asked by doing Bhakti! If you read Bhagavata for example, it says all those demons (including Putana) who were killed in the hands of Krishna attained moksha. Getting killed by God is a sure ticket to moksha. That is what even Bhishma said in the kurukshetra war when Krishna advanced to kill him!
2. If you look at the background of Ravana, he was one of the two door keepers of Vaukunta who were cursed to take human birth. Their only way of salvation was to hate God. Ravana did that and he attained freedom from his curse. He went back to God.

Now you choose which answer you want ;-)