Do not rely on actual NaN value for testing extractps.

BUG=cctest/test-assembler-ia32/AssemblerIa32Extractps, cctest/test-assembler-x64/AssemblerX64Extractps
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/26704004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17218 ce2b1a6d-e550-0410-aec6-3dcde31c8c00