drivers: net: Remove device_node checks with of_mdiobus_register()

A number of drivers have the following pattern:

if (np)
	of_mdiobus_register()
else
	mdiobus_register()

which the implementation of of_mdiobus_register() now takes care of.
Remove that pattern in drivers that strictly adhere to it.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Fugang Duan <fugang.duan@nxp.com>
Reviewed-by: Antoine Tenart <antoine.tenart@bootlin.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index b23c11d..2bb3f03 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -2454,10 +2454,7 @@ static int mv88e6xxx_mdio_register(struct mv88e6xxx_chip *chip,
 			return err;
 	}
 
-	if (np)
-		err = of_mdiobus_register(bus, np);
-	else
-		err = mdiobus_register(bus);
+	err = of_mdiobus_register(bus, np);
 	if (err) {
 		dev_err(chip->dev, "Cannot register MDIO bus (%d)\n", err);
 		mv88e6xxx_g2_irq_mdio_free(chip, bus);