drm_hwcomposer: make sure all fences are released for DrmDisplayComposition

This change will release the layers passed back to SurfaceFlinger even on an
error in the compositor thread.

Change-Id: I22f622855c8c953a058b4a08d0af1ae427e4cbbd
diff --git a/drmdisplaycomposition.h b/drmdisplaycomposition.h
index 09ad3ff..1df8dee 100644
--- a/drmdisplaycomposition.h
+++ b/drmdisplaycomposition.h
@@ -76,6 +76,7 @@
 
   int timeline_fd_;
   int timeline_;
+  int timeline_current_;
 
   DrmCompositionLayerVector_t layers_;
   uint32_t dpms_mode_;