power / charger-manager: unnecessary #include removed

extcon is going to include charger-manager.h and including
extcon.h at charger-manager is an overkill.

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
diff --git a/include/linux/power/charger-manager.h b/include/linux/power/charger-manager.h
index 0e86840..1214950 100644
--- a/include/linux/power/charger-manager.h
+++ b/include/linux/power/charger-manager.h
@@ -16,7 +16,7 @@
 #define _CHARGER_MANAGER_H
 
 #include <linux/power_supply.h>
-#include <linux/extcon.h>
+struct extcon_dev;
 
 enum data_source {
 	CM_BATTERY_PRESENT,