hwc2: enable the vsync on the display requested by SF

-- Avoid calculating the next vsync source based on the
  active display list in hwc2.
-- Enable/disable the vsync on the HWC display as requested
  by SurfaceFlinger.

Change-Id: I901be3d06ad1102d30232e6fb8dbb0d1709b5a68
CRs-fixed: 2429625
diff --git a/sdm/libs/hwc2/hwc_display_builtin.cpp b/sdm/libs/hwc2/hwc_display_builtin.cpp
index 53c9dc4..146d968 100644
--- a/sdm/libs/hwc2/hwc_display_builtin.cpp
+++ b/sdm/libs/hwc2/hwc_display_builtin.cpp
@@ -221,8 +221,9 @@
     hwc_layer->ResetBufferFlip();
   }
 
+  bool vsync_source = (callbacks_->GetVsyncSource() == id_);
   bool skip_commit = enable_drop_refresh_ && !pending_commit_ && !buffers_latched &&
-                     !pending_refresh_ && !vsync_source_;
+                     !pending_refresh_ && !vsync_source;
   pending_refresh_ = false;
 
   return skip_commit;