Greg Cosell says Ryan Mathews can be a “top five guy”

The Chargers haven’t kept it a secret this offseason that they want third-year tailback Ryan Mathews to handle a significant 2012 workload. Coach Norv Turner believes Mathews is “ready to take that next step,” and has likened Mathews to Ricky Williams, who carried the football 383 times in 2002 and 392 times in 2003, when…