quota: Store maximum space limit in bytes

Currently maximum space limit quota format supports is in blocks however
since we store space limits in bytes, this is somewhat confusing. So
store the maximum limit in bytes as well. Also rename the field to match
the new unit and related inode field to match the new naming scheme.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>