ANN ARBOR, Mich. — Michigan football has an embarrassment of riches in the running backs room. Led by Blake Corum and Donovan Edwards, the Wolverines have the best one-two punch in the country. But, as we saw last year, if one goes down, you need more bodies who can step up and take on the role. The Wolverines do have a few — converted linebacker Kalel Mullings performed well in the Big Ten Championship game, but fumbled in a key moment in the College Football Playoff semifinal; CJ Stokes was just a freshman last year, but looked good when inserted;…