net: usb: lan78xx: Fix memory leak on device unplug by freeing PHY device

Add calls to `phy_device_free` after `fixed_phy_unregister` to fix a
memory leak that occurs when the device is unplugged. This ensures
proper cleanup of pseudo fixed-link PHYs.

Fixes: 89b36fb ("lan78xx: Lan7801 Support for Fixed PHY")
Cc: Raghuram Chary J <raghuramchary.jallipalli@microchip.com>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20241116130558.1352230-2-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: olerem

drivers/net/usb/lan78xx.c

@@ -2380,6 +2380,7 @@ static int lan78xx_phy_init(struct lan78xx_net *dev)
 		if (dev->chipid == ID_REV_CHIP_ID_7801_) {
 			if (phy_is_pseudo_fixed_link(phydev)) {
 				fixed_phy_unregister(phydev);
+				phy_device_free(phydev);
 			} else {
 				phy_unregister_fixup_for_uid(PHY_KSZ9031RNX,
 							     0xfffffff0);
@@ -4246,8 +4247,10 @@ static void lan78xx_disconnect(struct usb_interface *intf)
 
 	phy_disconnect(net->phydev);
 
-	if (phy_is_pseudo_fixed_link(phydev))
+	if (phy_is_pseudo_fixed_link(phydev)) {
 		fixed_phy_unregister(phydev);
+		phy_device_free(phydev);
+	}
 
 	usb_scuttle_anchored_urbs(&dev->deferred);