iio: temperature: max30208: Remove an unused field in struct max30208_data

In "struct max30208_data", the 'indio_dev' field is unused.
Remove it.

Found with cppcheck, unusedStructMember.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/73f9f540ecdc7c10e833e6fc782324ae7d34ba9c.1714555144.git.christophe.jaillet@wanadoo.frSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/temperature/max30208.c

@@ -34,7 +34,6 @@
 
 struct max30208_data {
 	struct i2c_client *client;
-	struct iio_dev *indio_dev;
 	struct mutex lock; /* Lock to prevent concurrent reads of temperature readings */
 };