HOUSTON — It had always been about the seniors, the core of leaders who came back for one more season, one more shot at “natty-or-bust,” as running back Blake Corum pledged last season. Top-ranked Michigan (15-0) won the national championship on Monday night, before 72,808 at NRG Stadium, defeating Washington, 34-13. Corum scored two fourth-quarter touchdowns and defensive back Mike Sainristil made his sixth interception of the season to help seal the victory. Corum finished with 133 yards and two touchdowns and running back Donovan Edwards had 104 yards and two first-quarter two touchdowns, b…