[XFS] endianess annotations for xfs_dir2_data_entry_t

SGI-PV: 943272
SGI-Modid: xfs-linux-melb:xfs-kern:25806a

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Nathan Scott <nathans@sgi.com>