iio: chemical: ccs811: Fix output of IIO_CONCENTRATION channels

in_concentration_raw should report, according to sysfs-bus-iio documentation,
a "Raw (unscaled no offset etc.) percentage reading of a substance."

Modify scale to convert from ppm/ppb to percentage:
1 ppm = 0.0001%
1 ppb = 0.0000001%

There is no offset needed to convert the ppm/ppb to percentage,
so remove offset from IIO_CONCENTRATION (IIO_MOD_CO2) channel.

Cc'd stable to reduce chance of userspace breakage in the long
run as we fix this wrong bit of ABI usage.
Signed-off-by: Narcisa Ana Maria Vasile <narcisaanamaria12@gmail.com>
Cc: <Stable@vger.kernel.org>
Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/iio/chemical/ccs811.c

@@ -96,7 +96,6 @@ static const struct iio_chan_spec ccs811_channels[] = {
 		.channel2 = IIO_MOD_CO2,
 		.modified = 1,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
-				      BIT(IIO_CHAN_INFO_OFFSET) |
 				      BIT(IIO_CHAN_INFO_SCALE),
 		.scan_index = 0,
 		.scan_type = {
@@ -255,24 +254,18 @@ static int ccs811_read_raw(struct iio_dev *indio_dev,
 			switch (chan->channel2) {
 			case IIO_MOD_CO2:
 				*val = 0;
-				*val2 = 12834;
+				*val2 = 100;
 				return IIO_VAL_INT_PLUS_MICRO;
 			case IIO_MOD_VOC:
 				*val = 0;
-				*val2 = 84246;
-				return IIO_VAL_INT_PLUS_MICRO;
+				*val2 = 100;
+				return IIO_VAL_INT_PLUS_NANO;
 			default:
 				return -EINVAL;
 			}
 		default:
 			return -EINVAL;
 		}
-	case IIO_CHAN_INFO_OFFSET:
-		if (!(chan->type == IIO_CONCENTRATION &&
-		      chan->channel2 == IIO_MOD_CO2))
-			return -EINVAL;
-		*val = -400;
-		return IIO_VAL_INT;
 	default:
 		return -EINVAL;
 	}