Dev Patel, who made his screen debut in this year’s Oscar-favorite, “Slumdog Millionaire,” has signed for his next job. Patel has joined the cast of M. Night Shyamalan’s new movie, “The Last Airbender.”  Patel, who is replacing leaving actor Jesse McCartney, will play Zuko,a member of the Fire nation.  (And I have no idea what …