revalidate_disk_size just updates the block device size from the disk
size.  Thus calling it from virtblk_update_cache_mode doesn't actually
do anything.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NStefan Hajnoczi <stefanha@redhat.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>