HOT FLASHES: U2's Bono Hewson has a new passion--photography. According to friends, Hewson spent nearly two months in the autumn of 1985, traveling in Ethiopia, taking photos of children, landscapes and local communities. The Irish singer is putting the results on display next month as part of a three-week exhibit at Dublin's Hendriks Gallery. Hewson will show 30 photographs, which will be sold in signed and numbered limited-editions, with all proceeds going to organizations specializing in Third World famine relief. A gallery spokeswoman said they hope to raise as much as $1.5 million through the photo sales.