yasm: Fix a compile error introduced by my last commit. (Upstream at https://github.com/yasm/yasm/pull/63) TBR=fischman Review URL: https://chromiumcodereview.appspot.com/9669043 git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/yasm/patched-yasm@126079 4ff67af0-8c30-449e-8e8b-ad334ec8d88c