staging:iio:ad7780: add chip ID values and mask

The ad7780 supports both the ad778x and ad717x families. Each chip has
a corresponding ID. This patch provides a mask for extracting ID values
from the status bits and also macros for the correct values for the
ad7170, ad7171, ad7780 and ad7781.
Signed-off-by: Renato Lui Geh <renatogeh@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/adc/ad7780.c

@@ -30,6 +30,12 @@
 #define AD7780_ID0		BIT(3)
 #define AD7780_GAIN		BIT(2)
 
+#define AD7170_ID		0
+#define AD7171_ID		1
+#define AD7780_ID		1
+#define AD7781_ID		0
+
+#define AD7780_ID_MASK		(AD7780_ID0 | AD7780_ID1)
 
 #define AD7780_PATTERN_GOOD	1
 #define AD7780_PATTERN_MASK	GENMASK(1, 0)