The "err = " assignment is missing here.

Fixes: 0d65fc13 ('mlxsw: spectrum: Implement LAG port join/leave')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>