iio: ABI: Clarify proximity output value

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>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -1165,10 +1165,8 @@ Description:
 		object is near the sensor, usually be observing
 		reflectivity of infrared or ultrasound emitted.
 		Often these sensors are unit less and as such conversion
-		to SI units is not possible.  Where it is, the units should
-		be meters.  If such a conversion is not possible, the reported
-		values should behave in the same way as a distance, i.e. lower
-		values indicate something is closer to the sensor.
+		to SI units is not possible. Higher proximity measurements
+		indicate closer objects, and vice versa.
 
 What:		/sys/.../iio:deviceX/in_illuminance_input
 What:		/sys/.../iio:deviceX/in_illuminance_raw