net: ethernet: aquantia: Fixed missing rtnl_unlock.

rtnl_unlock should be called if error occurred.

Signed-off-by: Pavel Belous <pavel.belous@aquantia.com>
Reviewed-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>