net: dsa: bcm_sf2: Do not assume DSA master supports WoL

We assume in the bcm_sf2 driver that the DSA master network device
supports ethtool_ops::{get,set}_wol operations, which is not a given.
Avoid de-referencing potentially non-existent function pointers and
check them as we should.

Fixes: 96e65d7f ("net: dsa: bcm_sf2: add support for Wake-on-LAN")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/bcm_sf2.c

@@ -726,9 +726,10 @@ static void bcm_sf2_sw_get_wol(struct dsa_switch *ds, int port,
 {
 	struct net_device *p = ds->ports[port].cpu_dp->master;
 	struct bcm_sf2_priv *priv = bcm_sf2_to_priv(ds);
-	struct ethtool_wolinfo pwol;
+	struct ethtool_wolinfo pwol = { };
 
 	/* Get the parent device WoL settings */
+	if (p->ethtool_ops->get_wol)
 		p->ethtool_ops->get_wol(p, &pwol);
 
 	/* Advertise the parent device supported settings */
@@ -750,8 +751,9 @@ static int bcm_sf2_sw_set_wol(struct dsa_switch *ds, int port,
 	struct net_device *p = ds->ports[port].cpu_dp->master;
 	struct bcm_sf2_priv *priv = bcm_sf2_to_priv(ds);
 	s8 cpu_port = ds->ports[port].cpu_dp->index;
-	struct ethtool_wolinfo pwol;
+	struct ethtool_wolinfo pwol =  { };
 
+	if (p->ethtool_ops->get_wol)
 		p->ethtool_ops->get_wol(p, &pwol);
 	if (wol->wolopts & ~pwol.supported)
 		return -EINVAL;