Who you gonna call when you can’t keep an erection? Gerard Depardieu, that’s who. Seems Robert De Niro had that problem while shooting a scene for Bernardo Bertolucci’s “1900” back in 1977. To the rescue came Depardieu, who told the Montreal World Film Festival that his advice helped De Niro lick the problem, reports The Post’s V.A. Musetto. The secret, said Depardieu, involved water and Tiger Balm.