Luckily changing it back is fairly simple and can be done in a few easy steps:
- Navigate to your profile page and click on the "About" button just below your profile picture in Timeline.
- Scroll down to the "Contact Info" section and hit "Edit". You should get a drop down like the one below.
- On the far right of the image click on the drop down menu next to the circles. You want to switch the setting for your personal and your @facebook.com email addresses so that your personal one has "display on timeline" selected and the @facebook.com address has "hidden from timeline" selected.