Don Quixote had Sancho Panza. Wyatt Earp had Doc Holliday. Conan O’Brien has Andy Richter. And KBXX DJ Madd Hatta has James Garrett, better known to the ballers and shot-callers of H-town as Jay Mack. Every weekday, between 2 p.m. and 6 p.m., Mack serves as a right-hand man, a…