src/cmd/gc: fix some typos in the escape analysis comments
src/cmd/gc: fix some typos in the escape analysis comments

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7342044

apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,dsriram/golang,dsriram/golang,gnanderson/go,tv42/old-go,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,gnanderson/go,dsriram/golang,dsriram/golang,tv42/old-go,tv42/old-go,dsriram/golang,gnanderson/go,tv42/old-go,tv42/old-go,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,gnanderson/go,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme