igb: cleanup code related to ring resource allocation and free

This patch cleans up some of the ring alloc and free code to better handle
exceptions such as attempting to free resources on an already freed ring.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>