Revert "net: eth: cpsw: Correctly attach to GPIO bitbang MDIO driver"

This reverts commit f8d56d8f ("net:
 eth: cpsw: Correctly attach to GPIO bitbang MDIO driver").

Fix potential null-pointer dereference at probe if the mdio-gpio device
has not been successfully probed yet.

The offending commit is plain wrong for a number of reasons. First of
all it accesses internal driver data of an unrelated device. Neither
does it check that the data is non-null (which it is in case the device
has not been probed yet).

Furthermore, the decision on whether to treat any driver data according
to the mdio-gpio driver's internals is made based on the node name. But
the name is not compared against "mdio" which is the normal name for the
node, but rather against "gpio" which the node does not have to be named
(and shouldn't be according to the binding documentation). [ If this
hack is to be kept out-of-tree it should at least be matching against
the compatible property. ]

Cc: Stefan Roese <sr@denx.de>
Cc: stable <stable@vger.kernel.org>	# v3.14
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>