igb: use igb_free_q_vectors to cleanup failure in igb_alloc_q_vectors

This change makes it so that igb_free_q_vectors is reused in
igb_alloc_q_vectors to handle the cleanup instead of unwinding
through the allocations.

Signed-off-by: Nicholas Nunley <nicholasx.d.nunley@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>