bonding: bond_get_size() returns wrong size

There is an extra semi-colon so bond_get_size() doesn't return the
correct value.

Fixes: ec76aa49 ('bonding: add Netlink support active_slave option')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Veaceslav Falico <vfalico@redhat.com>
Reviewed-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>