Unreviewed trivial buildfix after r144190.

Patch by Csaba Osztrogonác <ossy@webkit.org> on 2013-02-27

* platform/graphics/surfaces/win/GraphicsSurfaceWin.cpp:
(WebCore::GraphicsSurface::platformPaintToTextureMapper):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144247 268f45cc-cd09-0410-ab3c-d52691b4dbfc