jfs: define xtree root and page independently

commit a779ed75 upstream.

In order to make array bounds checking sane, provide a separate
definition of the in-inode xtree root and the external xtree page.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Tested-by: Manas Ghandat <ghandatmanas@gmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=ccb458b6679845ee0bae


Reported-by:  <syzbot+ccb458b6679845ee0bae@syzkaller.appspotmail.com>
Signed-off-by: Aditya Dutt <duttaditya18@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>