net: bcmgenet: Properly configure PHY to ignore interrupt

By the time we execute bcmgenet_mii_probe(), the MDIO bus structure has
long been allocated and registered. Overirring the PHY interrupt using
the MDIO bus structure has no chance to work anymore, because
of_mdiobus_register() has call phy_device_create() for use, which copied
the MDIO bus address's irq for the PHY into the PHY device "irq" member.

Since we do have a proper reference to a PHY device in
bcmgenet_mii_probe(), just assign the desired IRQ value here.

Fixes: aa09677c

 ("net: bcmgenet: add MDIO routines")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>