net: phy: fixed: allow setting no update_link callback

fixed_phy_set_link_update() contains an early check against a NULL
callback pointer, which basically prevents us from removing any
previous callback we may have set. The users of the fp->link_update
callback deal with a NULL callback just fine, so we really want to allow
"removing" a link_update callback to avoid dangling callback pointers
during e.g: module removal.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/fixed_phy.c

@@ -168,7 +168,7 @@ int fixed_phy_set_link_update(struct phy_device *phydev,
 	struct fixed_mdio_bus *fmb = &platform_fmb;
 	struct fixed_phy *fp;
 
-	if (!link_update || !phydev || !phydev->bus)
+	if (!phydev || !phydev->bus)
 		return -EINVAL;
 
 	list_for_each_entry(fp, &fmb->phys, node) {