ab8500: Turn unneeded global symbols into local ones

The patch fixes the following sparse warning:

drivers/power/ab8500_charger.c:1619:6: warning: symbol 'ab8500_charger_detect_usb_type_work' was not declared. Should it be static?
drivers/power/abx500_chargalg.c:1709:24: warning: symbol 'abx500_chargalg_sysfs_ops' was not declared. Should it be static?
drivers/power/ab8500_fg.c:2328:24: warning: symbol 'ab8500_fg_sysfs_ops' was not declared. Should it be static?

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
diff --git a/drivers/power/ab8500_charger.c b/drivers/power/ab8500_charger.c
index a7217d6..e2b4acc 100644
--- a/drivers/power/ab8500_charger.c
+++ b/drivers/power/ab8500_charger.c
@@ -1616,7 +1616,7 @@
  *
  * Detect the type of USB plugged
  */
-void ab8500_charger_detect_usb_type_work(struct work_struct *work)
+static void ab8500_charger_detect_usb_type_work(struct work_struct *work)
 {
 	int ret;