net: dsa: mv88e6xxx: Add missing static to stub functions

Stub functions in header files need to be static, or we can have
multiple definitions errors.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Fixes: 6335e9f2446b ("net: dsa: mv88e6xxx: mv88e6390X SERDES support")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/global2.h

@@ -114,13 +114,13 @@ static inline int mv88e6xxx_g2_set_eeprom16(struct mv88e6xxx_chip *chip,
 	return -EOPNOTSUPP;
 }
 
-int mv88e6xxx_g2_pvt_write(struct mv88e6xxx_chip *chip, int src_dev,
-			   int src_port, u16 data)
+static int mv88e6xxx_g2_pvt_write(struct mv88e6xxx_chip *chip, int src_dev,
+				  int src_port, u16 data)
 {
 	return -EOPNOTSUPP;
 }
 
-int mv88e6xxx_g2_misc_4_bit_port(struct mv88e6xxx_chip *chip)
+static int mv88e6xxx_g2_misc_4_bit_port(struct mv88e6xxx_chip *chip)
 {
 	return -EOPNOTSUPP;
 }