A Cuban-born director whose work specializes in gritty urban realism, Leon Ichaso first made his mark with the independently made Spanish-language feature, "El Super" (1979), based on an Off-Broadway play about an immigrant building superintendent trying to make his way in New York City. It took six years for the filmmaker to follow up on this admirably honest and low-key study, but "Crossover Dreams" (1985), was a fine first shot at a somewhat more mainstream film. Marred somewhat by a conventional story of how a musician changes when he encounters success, the film was nonetheless an often