[EFL][WK2] Fix build warning after r142579
https://bugs.webkit.org/show_bug.cgi?id=109547

Patch by Jinwoo Song <jinwoo7.song@samsung.com> on 2013-02-12
Reviewed by Alexey Proskuryakov.

Use UNUSED_PARAM macro to fix -Wunused-parameter build warning.

* UIProcess/efl/PageViewportControllerClientEfl.cpp:
(WebKit::PageViewportControllerClientEfl::didChangeContentsSize):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142688 268f45cc-cd09-0410-ab3c-d52691b4dbfc