applications: nrf5340_audio: Audio module improvements

    Corrections from use, additional testing and fake function updates.

Signed-off-by: Graham Wacey <[email protected]>

tests/subsys/audio_module/src/audio_module_test_common.c

@@ -105,6 +105,7 @@ int test_data_process_function(struct audio_module_handle_private *handle,
 		audio_data_tx->data_size = audio_data_rx->data_size;
 	} else {
 		printk("The input and output data pointers are NULL");
+		return -1;
 	}
 
 	return 0;