iio: chemical: ccs811: Fix output of IIO_CONCENTRATION channels

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 <[email protected]>
Cc: <[email protected]>
Reviewed-by: Matt Ranostay <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>