xen/blocks: Return -EXX instead of -1

Lets return sensible values instead of -1.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/block/xen-blkback/xenbus.c

@@ -996,7 +996,7 @@ static int connect_ring(struct backend_info *be)
 		be->blkif->blk_protocol = BLKIF_PROTOCOL_X86_64;
 	else {
 		xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
-		return -1;
+		return -ENOSYS;
 	}
 	err = xenbus_gather(XBT_NIL, dev->otherend,
 			    "feature-persistent", "%u",

drivers/block/xen-blkfront.c

@@ -828,11 +828,11 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
 	info->tag_set.driver_data = info;
 
 	if (blk_mq_alloc_tag_set(&info->tag_set))
-		return -1;
+		return -EINVAL;
 	rq = blk_mq_init_queue(&info->tag_set);
 	if (IS_ERR(rq)) {
 		blk_mq_free_tag_set(&info->tag_set);
-		return -1;
+		return PTR_ERR(rq);
 	}
 
 	queue_flag_set_unlocked(QUEUE_FLAG_VIRT, rq);