iio: adc: axp20x_adc: fix charging current reporting on AXP22x

Both the charging and discharging currents on AXP22x are stored as
12-bit integers, in accordance with the datasheet.
It's also confirmed by vendor BSP (axp20x_adc.c:axp22_icharge_to_mA).

The scale factor of 0.5 is never mentioned in datasheet, nor in the
vendor source code. I think it was here to compensate for
erroneous addition bit in register width.

Tested on custom A40i+AXP221s board with external ammeter as
a reference.

Fixes: 0e34d5d ("iio: adc: add support for X-Powers AXP20X and AXP22X PMICs ADCs")
Signed-off-by: Evgeny Boger <boger@wirenboard.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Link: https://lore.kernel.org/r/20211116213746.264378-1-boger@wirenboard.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: evgeny-boger

drivers/iio/adc/axp20x_adc.c

@@ -251,19 +251,8 @@ static int axp22x_adc_raw(struct iio_dev *indio_dev,
 			  struct iio_chan_spec const *chan, int *val)
 {
 	struct axp20x_adc_iio *info = iio_priv(indio_dev);
-	int size;
 
-	/*
-	 * N.B.: Unlike the Chinese datasheets tell, the charging current is
-	 * stored on 12 bits, not 13 bits. Only discharging current is on 13
-	 * bits.
-	 */
-	if (chan->type == IIO_CURRENT && chan->channel == AXP22X_BATT_DISCHRG_I)
-		size = 13;
-	else
-		size = 12;
-
-	*val = axp20x_read_variable_width(info->regmap, chan->address, size);
+	*val = axp20x_read_variable_width(info->regmap, chan->address, 12);
 	if (*val < 0)
 		return *val;
 
@@ -386,9 +375,8 @@ static int axp22x_adc_scale(struct iio_chan_spec const *chan, int *val,
 		return IIO_VAL_INT_PLUS_MICRO;
 
 	case IIO_CURRENT:
-		*val = 0;
-		*val2 = 500000;
-		return IIO_VAL_INT_PLUS_MICRO;
+		*val = 1;
+		return IIO_VAL_INT;
 
 	case IIO_TEMP:
 		*val = 100;