net: dpaa2-mac: use correct interface to free mdiodev

Rather than using put_device(&mdiodev->dev), use the proper interface
provided to dispose of the mdiodev - that being mdio_device_free().

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Tested-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Link: https://lore.kernel.org/r/E1q2VsB-008QlZ-El@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>