SurfaceFlinger: fix wake up time when sf duration change

When SF changes its work duration, it may already have a scheduled
wake up callback. In this case the callback needs to be updated with the
new duration.

Bug: 172683933
Test: launch an app and observe systraces
Change-Id: Ie63cd5fa3f82f193cfba031bbbc0b4f8bf8086a9
diff --git a/services/surfaceflinger/TracedOrdinal.h b/services/surfaceflinger/TracedOrdinal.h
index 49cf80c..eee4bec 100644
--- a/services/surfaceflinger/TracedOrdinal.h
+++ b/services/surfaceflinger/TracedOrdinal.h
@@ -57,7 +57,9 @@
         trace();
     }
 
-    operator T() const { return mData; }
+    T get() const { return mData; }
+
+    operator T() const { return get(); }
 
     TracedOrdinal& operator=(T other) {
         mData = other;