cmd/compile: for non-SSA-typed params, emit simple vars.

This case was missed entirely and caused such params to be
unprintable.  This change gives them stack addresses
for the entire function (which is correct).

Change-Id: Ia4f706450219e48bce65b6395d3d9792df142fb5
Reviewed-on: https://go-review.googlesource.com/c/150657


Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>