Build fix to use the correct source.

Change-Id: If36710be600dd0e15c31682e0343f281baa55627
diff --git a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
index ca04495..c3d45ee 100644
--- a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
+++ b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
@@ -470,7 +470,7 @@
 
 void VirtualDisplaySurface::cancelBuffer(int pslot, const sp<Fence>& fence) {
     if (mDisplayId < 0)
-        return mSource[SOURCE_SINK]->cancelBuffer(mapProducer2SourceSlot(source, pslot), fence);
+        return mSource[SOURCE_SINK]->cancelBuffer(mapProducer2SourceSlot(SOURCE_SINK, pslot), fence);
 
     VDS_LOGW_IF(mDbgState != DBG_STATE_GLES,
             "Unexpected cancelBuffer(pslot=%d) in %s state", pslot,