rocker: fix an error code

We intended to return PTR_ERR() here instead of 1.

Fixes: 1f9993f6

 ('rocker: fix a neigh entry leak issue')
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>