staging: iio: ad7780: check if ad778x before gain update

Only the ad778x have the 'gain' status bit. Check it before updating
through a new variable is_ad778x in chip_info.
Signed-off-by: Giuliano Belinassi <giuliano.belinassi@usp.br>
Acked-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/adc/ad7780.c

@@ -35,6 +35,7 @@ struct ad7780_chip_info {
 	struct iio_chan_spec	channel;
 	unsigned int		pattern_mask;
 	unsigned int		pattern;
+	bool			is_ad778x;
 };
 
 struct ad7780_state {
@@ -113,10 +114,12 @@ static int ad7780_postprocess_sample(struct ad_sigma_delta *sigma_delta,
 	    ((raw_sample & chip_info->pattern_mask) != chip_info->pattern))
 		return -EIO;
 
+	if (chip_info->is_ad778x) {
 		if (raw_sample & AD7780_GAIN)
 			st->gain = 1;
 		else
 			st->gain = 128;
+	}
 
 	return 0;
 }
@@ -135,21 +138,25 @@ static const struct ad7780_chip_info ad7780_chip_info_tbl[] = {
 		.channel = AD7780_CHANNEL(12, 24),
 		.pattern = 0x5,
 		.pattern_mask = 0x7,
+		.is_ad778x = false,
 	},
 	[ID_AD7171] = {
 		.channel = AD7780_CHANNEL(16, 24),
 		.pattern = 0x5,
 		.pattern_mask = 0x7,
+		.is_ad778x = false,
 	},
 	[ID_AD7780] = {
 		.channel = AD7780_CHANNEL(24, 32),
 		.pattern = 0x1,
 		.pattern_mask = 0x3,
+		.is_ad778x = true,
 	},
 	[ID_AD7781] = {
 		.channel = AD7780_CHANNEL(20, 32),
 		.pattern = 0x1,
 		.pattern_mask = 0x3,
+		.is_ad778x = true,
 	},
 };