iio: ABI: Clarify proximity output value

iio: ABI: Clarify proximity output value

commit bdc10d57f236b534fb675a4bbefd10017aeb2b26 upstream.

Current description for proximity measurement is ambiguous. While
the first part says that proximity is measured by observing
reflectivity, the second part incorrectly infers that reported values
should behave like a distance.

This is because of AS3935 lightning sensor which uses the proximity
API, while not being a true proximity sensor.

Note this is marked for stable as it accompanies a fix in ABI usage
to the sx9500 driver which would otherwise appear to be correct.

Fixes:  614e8842ddf ("iio: ABI: add clarification for proximity")
Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>