Peter White Television EditorEXCLUSIVE: Marsai Martin, who plays Diane Johnson in the hit ABC comedy Black-ish, has teamed with Walden Media to adapt Ingrid Law’s children’s fantasy novel Savvy as a TV series.Martin’s Genius Entertainment, which has a first-look film deal with Universal Pictures, is developing the adaptation with The Chronicles of Narnia producer Walden Media.The book, which was published in 2008 by Penguin Random House and Walden Media, tells the story of Mibs Beaumont, who is