iio: adc: ad7793: Add missing error code in ad7793_setup()

Set error code while device ID query failed.

Fixes: 88bc3054 ("IIO: ADC: New driver for AD7792/AD7793 3 Channel SPI ADC")
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7793.c

@@ -279,6 +279,7 @@ static int ad7793_setup(struct iio_dev *indio_dev,
 	id &= AD7793_ID_MASK;
 
 	if (id != st->chip_info->id) {
+		ret = -ENODEV;
 		dev_err(&st->sd.spi->dev, "device ID query failed\n");
 		goto out;
 	}