loop: return proper error from loop_queue_rq()

->queue_rq() should return one of the BLK_MQ_RQ_QUEUE_* constants, not
an errno.

f4aa4c7b ("block: loop: convert to per-device workqueue")
Signed-off-by: Omar Sandoval <osandov@fb.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/loop.c

@@ -1646,7 +1646,7 @@ static int loop_queue_rq(struct blk_mq_hw_ctx *hctx,
 	blk_mq_start_request(bd->rq);
 
 	if (lo->lo_state != Lo_bound)
-		return -EIO;
+		return BLK_MQ_RQ_QUEUE_ERROR;
 
 	switch (req_op(cmd->rq)) {
 	case REQ_OP_FLUSH: