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

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang