net: davinci_emac: match the mdio device against its compatible if possible

[ Upstream commit ea0820bb771175c7d4192fc6f5b5c56b3c6d5239 ]

Device tree based systems without of_dev_auxdata will have the mdio
device named differently than "davinci_mdio(.0)". In this case use the
device's parent's compatible string for matching

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>