of_mdiobus_register is now called with nodes from ethernet devices.
Their child nodes are not necessarily phy nodes. For am335x devices
we get several warnings now:

miibus0: /ocp/ethernet@4a100000/mdio@4a101000 PHY address 1242566656 is too large
miibus0: /ocp/ethernet@4a100000/slave@4a100200 has invalid PHY address
miibus0: /ocp/ethernet@4a100000/slave@4a100300 has invalid PHY address
miibus0: /ocp/ethernet@4a100000/cpsw-phy-sel@44e10650 PHY address 1155597904 is too large

None of the nodes is a phy node, so silence the warnings and turn them
into dev_dbg.

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