xfs: avoid usage of struct xfs_dir2_block

In most places we can simply pass around and use the struct xfs_dir2_data_hdr,
which is the first and most important member of struct xfs_dir2_block instead
of the full structure.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

diff --cc fs/xfs/xfs_dir2_block.c
Simple merge

diff --cc fs/xfs/xfs_dir2_block.h
Simple merge

diff --cc fs/xfs/xfs_dir2_data.c
Simple merge

diff --cc fs/xfs/xfs_dir2_leaf.c
Simple merge

diff --cc fs/xfs/xfs_dir2_sf.c
Simple merge

diff --cc fs/xfs/xfs_dir2_sf.h
Simple merge