net: dsa: mv88e6xxx: fix non static symbol warnings

Fixes the following sparse warnings:

drivers/net/dsa/mv88e6xxx/chip.c:219:5: warning:
 symbol 'mv88e6xxx_port_read' was not declared. Should it be static?
drivers/net/dsa/mv88e6xxx/chip.c:227:5: warning:
 symbol 'mv88e6xxx_port_write' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: NVivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -216,16 +216,16 @@ int mv88e6xxx_write(struct mv88e6xxx_chip *chip, int addr, int reg, u16 val)
 	return 0;
 }
 
-int mv88e6xxx_port_read(struct mv88e6xxx_chip *chip, int port, int reg,
-			u16 *val)
+static int mv88e6xxx_port_read(struct mv88e6xxx_chip *chip, int port, int reg,
+			       u16 *val)
 {
 	int addr = chip->info->port_base_addr + port;
 
 	return mv88e6xxx_read(chip, addr, reg, val);
 }
 
-int mv88e6xxx_port_write(struct mv88e6xxx_chip *chip, int port, int reg,
-			 u16 val)
+static int mv88e6xxx_port_write(struct mv88e6xxx_chip *chip, int port, int reg,
+				u16 val)
 {
 	int addr = chip->info->port_base_addr + port;