ahci: remove dead reset code

This check is dead due to an earlier conditional.
AHCI does not currently support hotplugging, so
checks to see if devices are present or not are useless.

Remove it.

Reported-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1441140641-17631-2-git-send-email-jsnow@redhat.com
