iio: isl29018: fix to return error or 0 in isl29018_write_raw()

We had assigned the return value to 'ret' but ignored it when
return from isl29018_write_raw(), it's better to return 'ret'
instead of 0.

dpatch engine is used to auto generate this patch.
(https://github.com/weiyj/dpatch)

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/light/isl29018.c

@@ -356,7 +356,7 @@ static int isl29018_write_raw(struct iio_dev *indio_dev,
 	}
 	mutex_unlock(&chip->lock);
 
-	return 0;
+	return ret;
 }
 
 static int isl29018_read_raw(struct iio_dev *indio_dev,