Use the block layer helper to update both the disk and block device
sizes.  Contrary to the name no notification is sent in this case,
as a size 0 is special cased.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>