staging iio adt7410: sysfs store function must return length

Otherwise a write to the resolution entry never returns.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/adc/adt7410.c

@@ -257,7 +257,7 @@ static ssize_t adt7410_store_resolution(struct device *dev,
 
 	chip->config = config;
 
-	return ret;
+	return len;
 }
 
 static IIO_DEVICE_ATTR(resolution, S_IRUGO | S_IWUSR,