Merge pull request #3858 from OlegHahm/mutex_debug_tiny_fix

core mutex: use ATOMIC_VALUE for debug output

core/mutex.c

@@ -85,7 +85,7 @@ static void mutex_wait(struct mutex_t *mutex)
 void mutex_unlock(struct mutex_t *mutex)
 {
     unsigned irqstate = disableIRQ();
-    DEBUG("mutex_unlock(): val: %u pid: %" PRIkernel_pid "\n", mutex->val, sched_active_pid);
+    DEBUG("mutex_unlock(): val: %u pid: %" PRIkernel_pid "\n", ATOMIC_VALUE(mutex->val), sched_active_pid);
 
     if (ATOMIC_VALUE(mutex->val) == 0) {
         /* the mutex was not locked */