staging:iio: Move ad799x driver out of staging

The driver is now at a reasonable quality level. Move it out of staging.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --cc drivers/iio/adc/Kconfig
Simple merge

diff --cc drivers/iio/adc/Makefile
Simple merge

diff --cc drivers/iio/adc/ad799x.c
Simple merge

diff --cc drivers/staging/iio/adc/Kconfig
Simple merge

diff --cc drivers/staging/iio/adc/Makefile
Simple merge