The Dennis Hopper estate cleaned up this week at a Christie’s contemporary-art auction. The “Easy Rider” star, who died in May, was an avid collector as well as a painter and photographer himself. Forty works he owned, including pieces by Andy Warhol, Jean-Michel Basquiat and Keith Haring, fetched more than $10 million, almost double the minimum estimate. Hopper’s oldest daughter, Marin, and her co-executor, writer Alex Hitz, celebrated on Friday at Swifty’s on Lexington Avenue with investor Richard Turley. Despite the messy legal situation with Hopper’s wife, Victoria Duffy, who filed a $45 million claim against his estate, Marin confirmed that Hopper’s youngest child, 7-year-old Galen, will receive 40 percent of the estate to be held in trust. Lawyers for the Hopper estate couldn’t be reached.