iio: chemical: mhz19b: Fix error code in probe()

Return -ENOMEM if devm_iio_device_alloc() fails.  Don't return success.

Fixes: 4572a70 ("iio: chemical: Add support for Winsen MHZ19B CO2 sensor")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Acked-by: Gyeyoung Baek <gye976@gmail.com>
Link: https://patch.msgid.link/aBtZFLFlr0slcYSi@stanley.mountain
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: Dan Carpenter

drivers/iio/chemical/mhz19b.c

@@ -276,7 +276,7 @@ static int mhz19b_probe(struct serdev_device *serdev)
 
 	indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
 	if (!indio_dev)
-		return ret;
+		return -ENOMEM;
 	serdev_device_set_drvdata(serdev, indio_dev);
 
 	st = iio_priv(indio_dev);