net: dsa: bcm_sf2: drop priv->master_mii_dn

There used to be a of_node_put(priv->master_mii_dn) call in
bcm_sf2_mdio_unregister(), which was accidentally deleted in commit
6ca80638 ("net: dsa: Use conduit and user terms").

But it's not needed - we don't need to hold a reference on the
"brcm,unimac-mdio" OF node for that long, since we don't do anything
with it. We can release it as soon as we finish bcm_sf2_mdio_register().

Also reduce "if (err && dn)" to just "if (err)". We know "dn", aka the
former priv->master_mii_dn, is non-NULL. Otherwise, of_mdio_find_bus(dn)
would not have been able to find the bus behind "brcm,unimac-mdio".

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Tested-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>