HID: wacom: generic: Scale battery capacity measurements to percentages

The power_supply subsystem expects us to provide it with capacity values
measured in percent. In particular, AES devices (HID_DG_BATTERYSTRENGTH)
use the range 0-255, which needs to be rescaled. The MobileStudio Pro
(WACOM_HID_WD_BATTERY_LEVEL) uses the range 0-100, but there's no guarantee
that future devices will share the same range.
Signed-off-by: NJason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: NPing Cheng <ping.cheng@wacom.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_wac.c

@@ -1811,6 +1811,7 @@ static void wacom_wac_pad_battery_event(struct hid_device *hdev, struct hid_fiel
 
 	switch (equivalent_usage) {
 	case WACOM_HID_WD_BATTERY_LEVEL:
+		value = value * 100 / (field->logical_maximum - field->logical_minimum);
 		wacom_wac->hid_data.battery_capacity = value;
 		wacom_wac->hid_data.bat_connected = 1;
 		break;
@@ -2035,6 +2036,7 @@ static void wacom_wac_pen_event(struct hid_device *hdev, struct hid_field *field
 			wacom_wac->hid_data.sense_state = value;
 		return;
 	case HID_DG_BATTERYSTRENGTH:
+		value = value * 100 / (field->logical_maximum - field->logical_minimum);
 		wacom_wac->hid_data.battery_capacity = value;
 		wacom_wac->hid_data.bat_connected = 1;
 		break;