power: supply: axp20x_battery: properly report current when discharging

As stated in [1], negative current values are used for discharging
batteries.

AXP PMICs internally have two different ADC channels for shunt current
measurement: one used during charging and one during discharging.
The values reported by these ADCs are unsigned.
While the driver properly selects ADC channel to get the data from,
it doesn't apply negative sign when reporting discharging current.

[1] Documentation/ABI/testing/sysfs-class-power
Signed-off-by: Evgeny Boger <boger@wirenboard.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/axp20x_battery.c

@@ -186,7 +186,6 @@ static int axp20x_battery_get_prop(struct power_supply *psy,
 				   union power_supply_propval *val)
 {
 	struct axp20x_batt_ps *axp20x_batt = power_supply_get_drvdata(psy);
-	struct iio_channel *chan;
 	int ret = 0, reg, val1;
 
 	switch (psp) {
@@ -266,12 +265,12 @@ static int axp20x_battery_get_prop(struct power_supply *psy,
 		if (ret)
 			return ret;
 
-		if (reg & AXP20X_PWR_STATUS_BAT_CHARGING)
-			chan = axp20x_batt->batt_chrg_i;
-		else
-			chan = axp20x_batt->batt_dischrg_i;
-
-		ret = iio_read_channel_processed(chan, &val->intval);
+		if (reg & AXP20X_PWR_STATUS_BAT_CHARGING) {
+			ret = iio_read_channel_processed(axp20x_batt->batt_chrg_i, &val->intval);
+		} else {
+			ret = iio_read_channel_processed(axp20x_batt->batt_dischrg_i, &val1);
+			val->intval = -val1;
+		}
 		if (ret)
 			return ret;