Revert "drivers/net/phy/mdio-bitbang.c: Call mdiobus_unregister before mdiobus_free"

Revert "drivers/net/phy/mdio-bitbang.c: Call mdiobus_unregister before mdiobus_free"

This reverts commit b3fef60bcd4cf1988b713627ca6ebc1051510526.

As pointed out by Ben Hutchings, this change is not correct.

mdiobus_unregister() can't be called if the bus isn't registered yet,
however this change can result in situations which cause that to
happen.

Part of the confusion here revolves around the fact that the
callers of this module control registration/unregistration,
rather than the module itself.

Signed-off-by: David S. Miller <davem@davemloft.net>