crypto/dsa: gofmt

Somehow this file didn't get gofmted after the last change, which
interferes with merges.

Change-Id: I965cfdbf27a01124a6ed300be9687ff84f68f9a1
Reviewed-on: https://go-review.googlesource.com/35064


Reviewed-by: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Adam Langley <agl@chromium.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>