net: dsa: mv88e6xxx: fix non static symbol warning

Fixes the following sparse warning:

drivers/net/dsa/mv88e6xxx/chip.c:2866:5: warning:
 symbol 'mv88e6xxx_g1_set_switch_mac' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -2863,7 +2863,7 @@ static int mv88e6xxx_setup_port(struct mv88e6xxx_chip *chip, int port)
 	return mv88e6xxx_port_write(chip, port, PORT_DEFAULT_VLAN, 0x0000);
 }
 
-int mv88e6xxx_g1_set_switch_mac(struct mv88e6xxx_chip *chip, u8 *addr)
+static int mv88e6xxx_g1_set_switch_mac(struct mv88e6xxx_chip *chip, u8 *addr)
 {
 	int err;