don't use ->bd_inode to access the block device size

[Christoph Hellwig]

On Wed, Oct 13, 2021 at 07:10:13AM +0200, Christoph Hellwig wrote:
> I wondered about adding a helper for looking at the size in byte units
> to avoid the SECTOR_SHIFT shifts in various places.  But given that
> I could not come up with a good name and block devices fundamentally
> work in sector size granularity I decided against that.

So it seems like the biggest review feedback is that we should have
such a helper.  I think the bdev_size name is the worst as size does
not imply a particular unit.  bdev_nr_bytes is a little better but I'm
not too happy.  Any other suggestions or strong opinions?