Fix minor typos in platform-*.cc

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/146793002

Patch from Cosmin Truta <ctruta@blackberry.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18843 ce2b1a6d-e550-0410-aec6-3dcde31c8c00