NEW YORK — “SNL 1975,” a movie about the genesis of “Saturday Night Live,” has rounded out its cast to portray the original stars of the iconic NBC sketch comedy series. Lamorne Morris has been tapped to portray Garrett Morris, while Dylan O’Brien has landed the role of Dan Aykroyd in the Jason Reitman- helmed film. Meanwhile, Cory Michael Smith is set to play Chevy Chase and Matt Wood has been…