fix: use right var to prevent crash

src/multitasking/scheduler.c

@@ -20,7 +20,7 @@ static struct list *get_thread_to_switch(void)
 	it_t = current_tcb == NULL ? NULL : current_tcb->next;
 	while (it_p) {
 		while (it_t != NULL) {
-			if (it_t != NULL && CURRENT_TCB->state != WAITING)
+			if (it_t != NULL && ((struct tcb*)it_t->content)->state != WAITING)
 				return it_t;
 			it_t = it_t->next;
 		}