cmd/vet: fix up some nits in print.go found by kamil.kisiel@gmail.com
cmd/vet: fix up some nits in print.go found by kamil.kisiel@gmail.com

R=golang-dev, kamil.kisiel, bradfitz
CC=golang-dev
https://codereview.appspot.com/7369049

wesolows/golang,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old