[XFS] endianess annotate XFS_BMAP_BROOT_PTR_ADDR Make sure it returns a

__be64 and let the callers use the proper macros.

SGI-PV: 954580
SGI-Modid: xfs-linux-melb:xfs-kern:26560a

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nathan Scott <nathans@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>