staging: iio: ad7780: add missing switch default case

This patch simply adds a missing switch default case in read_raw.
Signed-off-by: Renato Lui Geh <renatogeh@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/adc/ad7780.c

@@ -118,6 +118,8 @@ static int ad7780_read_raw(struct iio_dev *indio_dev,
 	case IIO_CHAN_INFO_OFFSET:
 		*val = -(1 << (chan->scan_type.realbits - 1));
 		return IIO_VAL_INT;
+	default:
+		break;
 	}
 
 	return -EINVAL;