MIPS: Fix uses of range analysis results in HChange.

Port r19872 (6d8679b)

BUG=v8:3204
LOG=y
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/198973002

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19899 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
A64: Relax the register constraints for LSeqStringGetChar.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/197763006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19900 ce2b1a6d-e550-0410-aec6-3dcde31c8c00