PPC assembly pack: correct POWER9 results.

As it turns out originally published results were skewed by "turbo"
mode. VM apparently remains oblivious to dynamic frequency scaling,
and reports that processor operates at "base" frequency at all times.
While actual frequency gets increased under load.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6406)