Use the proper helper to read the block device size and switch various
places to pass the size in terms of sectors which is more practical.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211019062024.2171074-4-hch@lst.de
[axboe: fix comment typo]
Signed-off-by: Jens Axboe <axboe@kernel.dk>