appletalk: Set error code if register_snap_client failed

BugLink: https://bugs.launchpad.net/bugs/1858489

commit c93ad133 upstream.

If register_snap_client fails in atalk_init,
error code should be set, otherwise it will
triggers NULL pointer dereference while unloading
module.

Fixes: 9804501f ("appletalk: Fix potential NULL pointer dereference in unregister_snap_client")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/appletalk/ddp.c

@@ -1927,6 +1927,7 @@ static int __init atalk_init(void)
 	ddp_dl = register_snap_client(ddp_snap_id, atalk_rcv);
 	if (!ddp_dl) {
 		pr_crit("Unable to register DDP with SNAP.\n");
+		rc = -ENOMEM;
 		goto out_sock;
 	}