scsi_lib: untangle 0 and BLK_MQ_RQ_QUEUE_OK

Let's not depend on any of the BLK_MQ_RQ_QUEUE_* constants having
specific values. No functional change.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/scsi/scsi_lib.c

@@ -1810,7 +1810,7 @@ static inline int prep_to_mq(int ret)
 {
 	switch (ret) {
 	case BLKPREP_OK:
-		return 0;
+		return BLK_MQ_RQ_QUEUE_OK;
 	case BLKPREP_DEFER:
 		return BLK_MQ_RQ_QUEUE_BUSY;
 	default:
@@ -1897,7 +1897,7 @@ static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 	int reason;
 
 	ret = prep_to_mq(scsi_prep_state_check(sdev, req));
-	if (ret)
+	if (ret != BLK_MQ_RQ_QUEUE_OK)
 		goto out;
 
 	ret = BLK_MQ_RQ_QUEUE_BUSY;
@@ -1914,7 +1914,7 @@ static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 
 	if (!(req->rq_flags & RQF_DONTPREP)) {
 		ret = prep_to_mq(scsi_mq_prep_fn(req));
-		if (ret)
+		if (ret != BLK_MQ_RQ_QUEUE_OK)
 			goto out_dec_host_busy;
 		req->rq_flags |= RQF_DONTPREP;
 	} else {