rbd: mark block queue as non-rotational

Set QUEUE_FLAG_NONROT.  Following commit b277da0a ("block: disable
entropy contributions for nonrot devices") we should also clear
QUEUE_FLAG_ADD_RANDOM, but it's off by default for blk-mq drivers, so
just note it in the comment.

Also remove physical block size assignment - no sense in repeating
defaults that are not going to change.
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>

drivers/block/rbd.c

@@ -3762,8 +3762,8 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
 		goto out_tag_set;
 	}
 
-	/* We use the default size, but let's be explicit about it. */
-	blk_queue_physical_block_size(q, SECTOR_SIZE);
+	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
+	/* QUEUE_FLAG_ADD_RANDOM is off by default for blk-mq */
 
 	/* set io sizes to object size */
 	segment_size = rbd_obj_bytes(&rbd_dev->header);