mx-scroll-view: simplify shadow determination code
mx-scroll-view: simplify shadow determination code

pwithnall/mx,jonnylamb/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,clutter-project/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx,clutter-project/mx,pwithnall/mx