iio: core-trigger: make iio_device_register_trigger_consumer() an int return

Oddly enough the noop function is an int-return. This one seems to be void.
This change converts it to int, because we want to change how groups are
registered. With that change this function could error out with -ENOMEM.

Signed-off-by: Alexandru Ardelean <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/iio_core_trigger.h

···
 /**
  * iio_device_register_trigger_consumer() - set up an iio_dev to use triggers
  * @indio_dev: iio_dev associated with the device that will consume the trigger
+ *
+ * Return 0 if successful, negative otherwise
  **/
-void iio_device_register_trigger_consumer(struct iio_dev *indio_dev);
+int iio_device_register_trigger_consumer(struct iio_dev *indio_dev);
 
 /**
  * iio_device_unregister_trigger_consumer() - reverse the registration process

drivers/iio/industrialio-trigger.c

···
 }
 EXPORT_SYMBOL(iio_trigger_validate_own_device);
 
-void iio_device_register_trigger_consumer(struct iio_dev *indio_dev)
+int iio_device_register_trigger_consumer(struct iio_dev *indio_dev)
 {
 	indio_dev->groups[indio_dev->groupcounter++] =
 		&iio_trigger_consumer_attr_group;
+
+	return 0;
 }
 
 void iio_device_unregister_trigger_consumer(struct iio_dev *indio_dev)