ethernet: amd: au1000: Remove pointless warning

The warning about being able to read any MDIO device, not just the
attached ethernet devices PHY applies to all MDIO drivers. So remove
it. This also removes a reference to a member in phy_device which has
moved.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>