cmd/compile: run fmt on ssa

cmd/compile: run fmt on ssa

prove.go used to make my editor and precomit checks very unhappy.

Change-Id: I25f7ffa2191480bc1b4f91fa91ccf3e4768045fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/685818
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>