fix integration issue with 6eae1c4

Incorporate changes done for e5c7565i ("drm_hwcomposer: refactor Worker")

Change-Id: If2f14bdafb4d7e0c44e3afed978fb64a654e7ac0
diff --git a/vsyncworker.h b/vsyncworker.h
index 231fef2..787152e 100644
--- a/vsyncworker.h
+++ b/vsyncworker.h
@@ -41,7 +41,7 @@
   ~VSyncWorker() override;
 
   int Init(DrmResources *drm, int display);
-  int RegisterCallback(std::shared_ptr<VsyncCallback> callback);
+  void RegisterCallback(std::shared_ptr<VsyncCallback> callback);
 
   void VSyncControl(bool enabled);