exp/ssa: fix breakage due to https://code.google.com/p/go/source/detail?r=ca5e5de48173
exp/ssa: fix breakage due to https://code.google.com/p/go/source/detail?r=ca5e5de48173

I don't understand why this didn't show up during my testing.

R=bradfitz
TBR=bradfitz
CC=golang-dev
https://codereview.appspot.com/7237047

d0f/go-zh,mhennings/marcohennings-go,scirelli/scirelli-go,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,bryanxu/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,webfd/go-zh,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,bryanxu/go-zh,scirelli/scirelli-go,webfd/go-zh,rdp/rogerpack2005-golang,bryanxu/go-zh,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,scirelli/scirelli-go,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,mhennings/marcohennings-go,d0f/go-zh,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,bryanxu/go-zh,sanjosh/sanjos100-tipc,scirelli/scirelli-go,webfd/go-zh,scirelli/scirelli-go,rdp/rogerpack2005-golang,bryanxu/go-zh,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,d0f/go-zh,rdp/rogerpack2005-golang,mhennings/marcohennings-go,mhennings/marcohennings-go,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,rdp/rogerpack2005-golang,bryanxu/go-zh,mhennings/marcohennings-go,d0f/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,sanjosh/sanjos100-tipc,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,rdp/rogerpack2005-golang