tests/event: use EVENT_QUEUE_INIT_DETACHED

Changes the test so that EVENT_QUEUE_INIT_DETACHED is used for the initialization of detached event queue. Without this change, a compilation problem was not recognized for ESP8266, MSP430 and MIPS.

tests/events/main.c

@@ -128,7 +128,7 @@ int main(void)
     puts("[START] event test application.\n");
 
     /* test creation of delayed claiming of a detached event queue */
-    event_queue_t dq;
+    event_queue_t dq = EVENT_QUEUE_INIT_DETACHED;
     printf("initializing detached event queue %p\n", (void *)&dq);
     event_queue_init_detached(&dq);