staging:iio:ad7793: Use common Sigma Delta library

Convert the ad7793 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

@@ -111,8 +111,7 @@ config AD7780
 config AD7793
 	tristate "Analog Devices AD7792 AD7793 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
 	  AD7792 and AD7793 SPI analog to digital converters (ADC).

drivers/staging/iio/adc/ad7793.h

@@ -41,6 +41,7 @@
 
 /* Mode Register Bit Designations (AD7793_REG_MODE) */
 #define AD7793_MODE_SEL(x)	(((x) & 0x7) << 13) /* Operation Mode Select */
+#define AD7793_MODE_SEL_MASK	(0x7 << 13) /* Operation Mode Select mask */
 #define AD7793_MODE_CLKSRC(x)	(((x) & 0x3) << 6) /* ADC Clock Source Select */
 #define AD7793_MODE_RATE(x)	((x) & 0xF) /* Filter Update Rate Select */
 
@@ -70,6 +71,7 @@
 #define AD7793_CONF_REFSEL	(1 << 7) /* INT/EXT Reference Select */
 #define AD7793_CONF_BUF		(1 << 4) /* Buffered Mode Enable */
 #define AD7793_CONF_CHAN(x)	((x) & 0x7) /* Channel select */
+#define AD7793_CONF_CHAN_MASK	0x7 /* Channel select mask */
 
 #define AD7793_CH_AIN1P_AIN1M	0 /* AIN1(+) - AIN1(-) */
 #define AD7793_CH_AIN2P_AIN2M	1 /* AIN2(+) - AIN2(-) */