Replace IInterface::asBinder() with a static

so we can do NULL checks again, and update calls to IInterface::asBinder()
to use the new static version.

Change-Id: Ia7b10eb38ca55b72278bfd33d3bf647f338b4e6a
diff --git a/libs/gui/SurfaceControl.cpp b/libs/gui/SurfaceControl.cpp
index 7597c99..61011b9 100644
--- a/libs/gui/SurfaceControl.cpp
+++ b/libs/gui/SurfaceControl.cpp
@@ -176,7 +176,7 @@
     if (control != NULL) {
         bp = control->mGraphicBufferProducer;
     }
-    return parcel->writeStrongBinder(bp->asBinder());
+    return parcel->writeStrongBinder(IInterface::asBinder(bp));
 }
 
 sp<Surface> SurfaceControl::getSurface() const