go.tools/ssa: use correct Alloc.Comment in lifting.
go.tools/ssa: use correct Alloc.Comment in lifting.

(Only affects diagnostic output.)

R=gri, gri
CC=golang-dev
https://codereview.appspot.com/23770046

t-yuki/go.tools.old,t-yuki/go.tools.old,t-yuki/go.tools.old