ds2781_battery: w1_ds2781_read() should be static

This patch fixes the following sparse warning:

  CHECK   drivers/power/ds2781_battery.c
drivers/power/ds2781_battery.c:72:5: warning: symbol 'w1_ds2781_read' was not declared. Should it be static?
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>

drivers/power/ds2781_battery.c

@@ -69,7 +69,7 @@ static inline int ds2781_battery_io(struct ds2781_device_info *dev_info,
 		return w1_ds2781_io(dev_info->w1_dev, buf, addr, count, io);
 }
 
-int w1_ds2781_read(struct ds2781_device_info *dev_info, char *buf,
+static int w1_ds2781_read(struct ds2781_device_info *dev_info, char *buf,
 		int addr, size_t count)
 {
 	return ds2781_battery_io(dev_info, buf, addr, count, 0);