iio:ad5686: Report scale as fractional value

Move the complexity of calculating the fixed point scale to the core.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/dac/ad5686.c

@@ -201,7 +201,6 @@ static int ad5686_read_raw(struct iio_dev *indio_dev,
 			   long m)
 {
 	struct ad5686_state *st = iio_priv(indio_dev);
-	unsigned long scale_uv;
 	int ret;
 
 	switch (m) {
@@ -214,12 +213,9 @@ static int ad5686_read_raw(struct iio_dev *indio_dev,
 		*val = ret;
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
-		scale_uv = (st->vref_mv * 100000)
-			>> (chan->scan_type.realbits);
-		*val =  scale_uv / 100000;
-		*val2 = (scale_uv % 100000) * 10;
-		return IIO_VAL_INT_PLUS_MICRO;
-
+		*val = st->vref_mv;
+		*val2 = chan->scan_type.realbits;
+		return IIO_VAL_FRACTIONAL_LOG2;
 	}
 	return -EINVAL;
 }