net/davinci_emac: fix failing PHY connect attempts

PHY connect attempts fail if no PHY id is specified in the emac platform
data and another mdio bus has been registered before 'davinci_mdio' bus. In
this case when configuring the interface, there will be an attempt to
connect to already attached PHY on the previously registered mdio bus:

net eth1: PHY already attached
net eth1: could not connect to phy smsc911x-0:01
IP-Config: Failed to open eth1
IP-Config: Device `eth1' not found

Fix this by modifying match_first_device() to match first PHY device
on 'davinci_mdio' bus.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>