[optimizing] Address x86_64 RIP patch comments

Nicolas had some comments after the patch
https://android-review.googlesource.com/#/c/144100

 had merged.  Fix the
problems that he found.

Change-Id: I40e8a4273997860db7511dc8f1986281b72bead2
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>