Amma Kanakku, the Tamil adaptation of the Hindi movie Nil Battey Sannata, is a heartwarming drama—the sort of story that leaves you feeling good—even though it addresses an important theme: the necessity of having goals. It’s a well-meaning film that mostly manages to steer clear of the overly sentimental melodrama common in films with similar messages, although it does fall into this trap toward the conclusion. T…