ppc64/ppc64asm: fix nits found by vet

Part of the Sisyphean goal of keeping vet happy
with the main Go repo.

Change-Id: I706b4d79066396a1ab5207f5b86dbb3d1a30d8b4
Reviewed-on: https://go-review.googlesource.com/31756
Reviewed-by: Minux Ma <minux@golang.org>
2 files changed