iio:adc:ad7766: Fix unnecessary check in ad7766_probe()

In the function ad7766_probe(), the return value of
devm_iio_device_register() can be zero or ret, Thus it
is unnecessary to repeated check here.
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Signed-off-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>
Co-developed-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20210511134739.948-1-tangbin@cmss.chinamobile.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7766.c

@@ -290,10 +290,7 @@ static int ad7766_probe(struct spi_device *spi)
 	if (ret)
 		return ret;
 
-	ret = devm_iio_device_register(&spi->dev, indio_dev);
-	if (ret)
-		return ret;
-	return 0;
+	return devm_iio_device_register(&spi->dev, indio_dev);
 }
 
 static const struct spi_device_id ad7766_id[] = {