iio:trigger: device_unregister->device_del to avoid double free

iio_trigger unregistration and freeing has been separated in this
code for some time, but it looks like the calls to the device
handling were not appropriately updated.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Reported-by: Otavio Salvador <otavio@ossystems.com.br>
Tested-by: Otavio Salvador <otavio@ossystems.com.br>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>

drivers/iio/industrialio-trigger.c

@@ -104,7 +104,7 @@ void iio_trigger_unregister(struct iio_trigger *trig_info)
 
 	ida_simple_remove(&iio_trigger_ida, trig_info->id);
 	/* Possible issue in here */
-	device_unregister(&trig_info->dev);
+	device_del(&trig_info->dev);
 }
 EXPORT_SYMBOL(iio_trigger_unregister);