ethernet: sun: add check for the mdesc_grab()

In vnet_port_probe() and vsw_port_probe(), we should
check the return value of mdesc_grab() as it may
return NULL which can caused NPD bugs.

Fixes: 5d01fa0c6b ("ldmvsw: Add ldmvsw.c driver code")
Fixes: 43fdf27470 ("[SPARC64]: Abstract out mdesc accesses for better MD update handling.")
Signed-off-by: Liang He <windhl@126.com>
Reviewed-by: Piotr Raczynski <piotr.raczynski@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sun/ldmvsw.c

@@ -287,6 +287,9 @@ static int vsw_port_probe(struct vio_dev *vdev, const struct vio_device_id *id)
 
 	hp = mdesc_grab();
 
+	if (!hp)
+		return -ENODEV;
+
 	rmac = mdesc_get_property(hp, vdev->mp, remote_macaddr_prop, &len);
 	err = -ENODEV;
 	if (!rmac) {

drivers/net/ethernet/sun/sunvnet.c

@@ -433,6 +433,9 @@ static int vnet_port_probe(struct vio_dev *vdev, const struct vio_device_id *id)
 
 	hp = mdesc_grab();
 
+	if (!hp)
+		return -ENODEV;
+
 	vp = vnet_find_parent(hp, vdev->mp, vdev);
 	if (IS_ERR(vp)) {
 		pr_err("Cannot find port parent vnet\n");