block: move sync_blockdev from __blkdev_put to blkdev_put

Do the early unlocked syncing even earlier to move more code out of
the recursive path.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20210525061301.2242282-3-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>