Danny DeVito worked hard for his dinner at The Spotted Pig the other night. The pint-size comedian came into the West Village eatery for dinner Friday with some cast members and friends from his FX sitcom, “It’s Always Sunny in Philadelphia.” But after eating, DeVito hopped into the kitchen to help plate up meals and hang out with the bar staff. “He just wandered in and asked if he could help,” said a spy. “He was entertaining all of the customers on the first floor of the restaurant and the cooks.” The actor — who recently reconciled with his wife, Rhea Perlman, after splitting last year — then posed for photos with the kitchen staff.