xfs_repair: Remove BUF_PTR from attr_repair.c

xfs_repair: Remove BUF_PTR from attr_repair.c

The BUF_PTR macro was removed from kernelspace a while ago
(6292604 xfs: Remove the macro XFS_BUF_PTR) but it lives
on in some parts of xfsprogs.  dir2.c doesn't use it,
but similar code in attr_repair.c does.  remove it from
attr_repair.c to converge the code.

Remove a related but unnecessary cast from a *void b_addr
in dir2.c while we're at it.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>