staging:iio:ad7192: Use common Sigma Delta library

Convert the ad7192 driver to make use of the new common code for devices from
the Analog Devices Sigma Delta family.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/adc/Kconfig

@@ -131,8 +131,7 @@ config AD7816
 config AD7192
 	tristate "Analog Devices AD7190 AD7192 AD7195 ADC driver"
 	depends on SPI
-	select IIO_BUFFER
-	select IIO_TRIGGERED_BUFFER
+	select AD_SIGMA_DELTA
 	help
 	  Say yes here to build support for Analog Devices AD7190,
 	  AD7192 or AD7195 SPI analog to digital converters (ADC).