net: phy: replace PHY_HAS_INTERRUPT with a check for config_intr and ack_interrupt

Flag PHY_HAS_INTERRUPT is used only here for this small check. I think
using interrupts isn't possible if a driver defines neither
config_intr nor ack_interrupts callback. So we can replace checking
flag PHY_HAS_INTERRUPT with checking for these callbacks.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>