Third-rate GODFATHER clone is so clearly patterned after the Francis Coppola blockbuster that the end result, despite the occasional felicities, is doubly disappointing: Tomas Milian, the consigliori of the title, naturally has the Robert Duvall role; Martin Balsam steps in for Brando as the Don and also suffers an attempt on his life (while visiting his wife’s grave); there is…