Fixed build error introduced by test upgrade without code upgrade.

Change-Id: If0dc93c9013ccd1898fb1ec7eb34b355772d6b82
diff --git a/aos/linux_code/ipc_lib/mutex.cpp b/aos/linux_code/ipc_lib/mutex.cpp
index 8c98204..4bd0759 100644
--- a/aos/linux_code/ipc_lib/mutex.cpp
+++ b/aos/linux_code/ipc_lib/mutex.cpp
@@ -17,9 +17,11 @@
 // Lock and Unlock use the return values of mutex_lock/mutex_unlock
 // to determine whether the lock/unlock succeeded.
 
-void Mutex::Lock() {
+bool Mutex::Lock() {
   if (mutex_grab(&impl_) != 0) {
     PLOG(FATAL, "mutex_grab(%p(=%" PRIu32 ")) failed", &impl_, impl_);
+  } else {
+    return false;
   }
 }