We added another error condition here, but if we were to hit it then
we need to unregister_netdev() before doing the free_netdev().
Otherwise we would hit the BUG_ON() in free_netdev():

	BUG_ON(dev->reg_state != NETREG_UNREGISTERED);
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Tested-by: NRaffaele Recalcati <raffaele.recalcati@bticino.it>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>