switchdev: fix: pass correct obj size when deferring obj add

Fixes: 4d429c5d ("switchdev: introduce possibility to defer obj_add/del")
Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>