xfs: convert dir byte/off conversion to xfs_da_geometry

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --cc fs/xfs/xfs_dir2.c
Simple merge

diff --cc fs/xfs/xfs_dir2_priv.h
Simple merge

diff --cc fs/xfs/xfs_dir2_readdir.c
Simple merge