net: usb: lan78xx: lan78xx_phy_init(): use PHY_POLL instead of "0" if no IRQ is available

On most systems request for IRQ 0 will fail, phylib will print an error message
and fall back to polling. To fix this set the phydev->irq to PHY_POLL if no IRQ
is available.

Fixes: cc89c323a3 ("lan78xx: Use irq_domain for phy interrupt from USB Int. EP")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Sven Schuchmann <schuchmann@schleissheimer.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/lan78xx.c

@@ -2228,7 +2228,7 @@ static int lan78xx_phy_init(struct lan78xx_net *dev)
 	if (dev->domain_data.phyirq > 0)
 		phydev->irq = dev->domain_data.phyirq;
 	else
-		phydev->irq = 0;
+		phydev->irq = PHY_POLL;
 	netdev_dbg(dev->net, "phydev->irq = %d\n", phydev->irq);
 
 	/* set to AUTOMDIX */