ppc assembly pack: always increment CTR IV as quadword

The kernel self-tests picked up an issue with CTR mode. The issue was
detected with a test vector with an IV of
FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFD: after 3 increments it should wrap
around to 0.

There are two paths that increment IVs: the bulk (8 at a time) path,
and the individual path which is used when there are fewer than 8 AES
blocks to process.

In the bulk path, the IV is incremented with vadduqm: "Vector Add
Unsigned Quadword Modulo", which does 128-bit addition.

In the individual path, however, the IV is incremented with vadduwm:
"Vector Add Unsigned Word Modulo", which instead does 4 32-bit
additions. Thus the IV would instead become
FFFFFFFFFFFFFFFFFFFFFFFF00000000, throwing off the result.

Use vadduqm.

This was probably a typo originally, what with q and w being
adjacent.

CLA: trivial

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8942)