net: pcs: lynx: remove lynx_get_mdio_device()

commit  b04fe5168fa9ccb1a654f577572062ffa93cb4d7 from
https://github.com/nxp-imx/linux-imx lf-6.1.y

lynx_get_mdio_device() is no longer necessary, let's remove it so the
lynx PCS code is always managing the lifetime of the mdiodev.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit b3b984dc

)
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>