Fix error reporting in Surface::cancelBuffer()

when we validate the surface there, most errors are in fact allowed
because it is legal to cancel a buffer after a surface has been
destroyed (for instance). in that case make sure to not log
error messages as they are very confusing.

Change-Id: Iecdfbaf6d9ee5da54d56cd7ea7a0d430c30934b0
diff --git a/include/surfaceflinger/Surface.h b/include/surfaceflinger/Surface.h
index 2df8ca3..5532052 100644
--- a/include/surfaceflinger/Surface.h
+++ b/include/surfaceflinger/Surface.h
@@ -233,7 +233,7 @@
      *  private stuff...
      */
     void init();
-    status_t validate() const;
+    status_t validate(bool inCancelBuffer = false) const;
     sp<ISurface> getISurface() const;
 
     inline const GraphicBufferMapper& getBufferMapper() const { return mBufferMapper; }