libqos/ahci: edit wait to be ncq aware

The wait command should check to make sure SACT is clear as well
as the Command Issue register.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1435016308-6150-12-git-send-email-jsnow@redhat.com
