bonding: fix error return code in bond_enslave()

Fix to return a negative error code in the add bond vlan ids error
handling case instead of 0, as done elsewhere in this function.

Introduced by commit 1ff412ad.
(bonding: change the bond's vlan syncing functions with the standard ones)

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>