commit 25937580 upstream.

Since we will return enum ata_completion_errors from qc_prep in the next
patch, let's define AC_ERR_OK to mark the OK status.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-ide@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>