Staging: iio: adc: Update Kconfig entries adding module name information

This patch fixes the following checkpatch.pl warning:

WARNING: please write a paragraph that describes the config symbol fully

Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>