power: supply: twl4030-charger: make twl4030_bci_property_is_writeable static

The function twl4030_bci_property_is_writeable can be made static
as it does not need to be in global scope.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Tested-by: "H. Nikolaus Schaller" <hns@goldelico.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>

drivers/power/supply/twl4030_charger.c

@@ -943,7 +943,7 @@ static int twl4030_bci_set_property(struct power_supply *psy,
 	return 0;
 }
 
-int twl4030_bci_property_is_writeable(struct power_supply *psy,
+static int twl4030_bci_property_is_writeable(struct power_supply *psy,
 				      enum power_supply_property psp)
 {
 	switch (psp) {