net: dsa: mv88e6xxx: mask apparently non-existing phys during probing

To avoid excessive mdio bus transactions during probing, mask all phy
addresses that do not exist (there is a 1:1 mapping between switch port
number and phy address).

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Klaus Kudielka <klaus.kudielka@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -3805,6 +3805,7 @@ static int mv88e6xxx_mdio_register(struct mv88e6xxx_chip *chip,
 	bus->read_c45 = mv88e6xxx_mdio_read_c45;
 	bus->write_c45 = mv88e6xxx_mdio_write_c45;
 	bus->parent = chip->dev;
+	bus->phy_mask = GENMASK(31, mv88e6xxx_num_ports(chip));
 
 	if (!external) {
 		err = mv88e6xxx_g2_irq_mdio_setup(chip, bus);