This makes of_phy_device_connect() work properly when the phy is
specified in the device tree. Without it of_mdio_find_phy() will
not find the right device. It will match:

bus->parent->device_node == phy_node->parent

Without this patch bus->parent->device_node will be the ethernet node
and phy_node->parent will be the ti,cpsw-mdio node. With the MDIO device
node registered as device of its own both nodes above will be the
ti,cpsw-mdio node.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>