IB/IPoIB: Fix error code in ipoib_add_port()

We accidentally don't see the error code on some of these error paths.
It means we return ERR_PTR(0) which is NULL and it results in a NULL
dereference in the caller.

This bug dates to pre-git days.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>

drivers/infiniband/ulp/ipoib/ipoib_main.c

@@ -2239,6 +2239,7 @@ static struct net_device *ipoib_add_port(const char *format,
 		goto register_failed;
 	}
 
+	result = -ENOMEM;
 	if (ipoib_cm_add_mode_attr(priv->dev))
 		goto sysfs_failed;
 	if (ipoib_add_pkey_attr(priv->dev))