You don’t need to believe in the generosity of an ancient water deity to be transfixed by Nigerian director C.J. “Fiery” Obasi’s folklore melodrama “Mami Wata.” Respecting the conjuring power of movies is all the devotion that’s required to fall under the spell cast by Obasi’s stark, roiling tale of spirit-world mysteries and all-too-human machinations, filmed in an evocatively dense …
