xfs: remove the ->data_dot_entry_p and ->data_dotdot_entry_p methods

xfs: remove the ->data_dot_entry_p and ->data_dotdot_entry_p methods

The only user of the ->data_dot_entry_p and ->data_dotdot_entry_p
methods is the xfs_dir2_sf_to_block function that builds block format
directorys from a short form directory.  It already uses pointer
arithmetics with a offset variable to do so for the real entries in
the directory, so switch the generation of the . and .. entries to
the same scheme, and clean up some of the later pointer arithmetics
to use bp->b_addr directly as well and avoid some casts.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>