Fix layout test for blending in the background
https://bugs.webkit.org/show_bug.cgi?id=113402

Patch by Mirela Budaes <mbudaes@adobe.com> on 2013-03-28
Reviewed by Dirk Schulze.

Fixed the layout test effect-background-blend-mode.html typo
Also rebaselined the test

* css3/compositing/effect-background-blend-mode.html:
* platform/mac/css3/compositing/effect-background-blend-mode-expected.png:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147128 268f45cc-cd09-0410-ab3c-d52691b4dbfc