The ratings have been consistently high, and yes, the ratings have dipped just a bit. It's still mostly high and we have the season finale to go through, I'm sure season three would still maintain good and steady 2 Broke Girls ratings.
Like what sugarydonught said, this is just a minor bump. The ratings won't severley drop because it has good writing and funny lines (like what nothingorall said). It will probably end in season 3 and it will contain healthy ratings, so they it gets renewed for season 4