net/bridge: use kobject_put to release kobject in br_add_if error path

kobject_init_and_add will alloc memory for kobj->name, so in br_add_if
error path, simply use kobject_del will not free memory for kobj->name.
Fix by using kobject_put instead, kobject_put will internally calls
kobject_del and frees memory for kobj->name.

Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>