[x86] Fix register constraints for multiply-high.

TEST=mjsunit/compiler,unittests
R=titzer@chromium.org

Review URL: https://codereview.chromium.org/671393002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24862 ce2b1a6d-e550-0410-aec6-3dcde31c8c00