Fixed jump in non-SSE4.1 implementation of LMathFloor instruction on x64.

BUG=chromium:370384
LOG=N
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/261853009

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21171 ce2b1a6d-e550-0410-aec6-3dcde31c8c00