Lan78xx driver accesses the PHY registers through MDIO bus over USB
connection. When performing a suspend/resume, the PHY registers can be
accessed before the USB connection is resumed. This will generate an
error and will prevent the device to resume correctly.
This patch adds the dependency between the MDIO bus and USB device to
allow correct handling of suspend/resume.

Fixes: ce85e13a ("lan78xx: Update to use phylib instead of mii_if_info.")
Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>