[8021Q]: vlan_ioctl_handler: fix return value

net/8021q/vlan.c: In function 'vlan_ioctl_handler':
net/8021q/vlan.c:700: warning: 'err' may be used uninitialized in this function

The warning is incorrect, but from my reading this ioctl will return -EINVAL
on success.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>