net: dsa: realtek: clean user_mii_bus setup

Remove the line assigning dev.of_node in mdio_bus as subsequent
of_mdiobus_register will always overwrite it.

As discussed in [1], allow the DSA core to be simplified, by not
assigning ds->user_mii_bus when the MDIO bus is described in OF, as it
is unnecessary.

Since commit 3b73a7b8 ("net: mdio_bus: add refcounting for fwnodes
to mdiobus"), we can put the "mdio" node just after the MDIO bus
registration.

[1] https://lkml.kernel.org/netdev/20231213120656.x46fyad6ls7sqyzv@skbuf/T/#u



Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>