xfs: remove m_litino

With the upcoming v3 inodes the inode data/attr area size needs to be
calculated for each specific inode, so we can't cache it in the superblock
anymore.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Felix Blyakher <felixb@sgi.com>