phy: mdio: fix memory leak

In the Linux kernel, the following vulnerability has been resolved:

phy: mdio: fix memory leak

Syzbot reported memory leak in MDIO bus interface, the problem was in

wrong state logic.

MDIOBUS_ALLOCATED indicates 2 states:

1. Bus is only allocated

2. Bus allocated and __mdiobus_register() fails, but

device_register() was called

In case of device_register() has been called we should call put_device()

to correctly free the memory allocated for this device, but mdiobus_free()

calls just kfree(dev) in case of MDIOBUS_ALLOCATED state

To avoid this behaviour we need to set bus->state to MDIOBUS_UNREGISTERED

_before_ calling device_register(), because put_device() should be

called even in case of device_register() failure.