MIPS: Rename ascii to one-byte where applicable.

Port r23840 (5463c43)

BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/542193003

Patch from Balazs Kilvady <balazs.kilvady@imgtec.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23848 ce2b1a6d-e550-0410-aec6-3dcde31c8c00