net: usb: asix_devices: add phy_mask for ax88772 mdio bus

Without setting phy_mask for ax88772 mdio bus, current driver may create
at most 32 mdio phy devices with phy address range from 0x00 ~ 0x1f.
DLink DUB-E100 H/W Ver B1 is such a device. However, only one main phy
device will bind to net phy driver. This is creating issue during system
suspend/resume since phy_polling_mode() in phy_state_machine() will
directly deference member of phydev->drv for non-main phy devices. Then
NULL pointer dereference issue will occur. Due to only external phy or
internal phy is necessary, add phy_mask for ax88772 mdio bus to workarnoud
the issue.

Closes: https://lore.kernel.org/netdev/20250806082931.3289134-1-xu.yang_2@nxp.com
Fixes: e532a09 ("net: usb: asix: ax88772: add phylib support")
Cc: stable@vger.kernel.org
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20250811092931.860333-1-xu.yang_2@nxp.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: Xu Yang

drivers/net/usb/asix_devices.c

@@ -676,6 +676,7 @@ static int ax88772_init_mdio(struct usbnet *dev)
 	priv->mdio->read = &asix_mdio_bus_read;
 	priv->mdio->write = &asix_mdio_bus_write;
 	priv->mdio->name = "Asix MDIO Bus";
+	priv->mdio->phy_mask = ~(BIT(priv->phy_addr) | BIT(AX_EMBD_PHY_ADDR));
 	/* mii bus name is usb-<usb bus number>-<usb device number> */
 	snprintf(priv->mdio->id, MII_BUS_ID_SIZE, "usb-%03d:%03d",
 		 dev->udev->bus->busnum, dev->udev->devnum);