CLEVER girl that Laura Patten. While Dad is back home in London, his mind pre-occupied with other things, she drops the news that she plans to backpack around the world with some friends. Governor Chris Patten's lively daughter will probably call by at her Hongkong pied-a-terre - Government House - on her travels to personally inquire of the chefs what they've done to Dad's waistline. ''They must have done something recently because Dad's lost so much weight. I think it's brilliant,'' she enthused to a British newspaper. Now experimenting with a new hair-do, Laura also confessed to the newspaper that she was yet to find her niche: ''I know I want to succeed, but I don't know at what. I'm a very confused young girl.'' Not half as confused as Dad is when dealing with the Chinese, Laura dear.