[arm64] Bug fix in sapefoint recording.
[arm64] Bug fix in sapefoint recording.

cp is handled by the register allocator and doesn't necessarily hold the
context pointer on arm64.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/695323005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#25209}
git-svn-id: f98b9d40cb02301bc76fa9e1b46ee668158567fd@25209 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh