gfs2: Truncate address space when flipping GFS2_DIF_JDATA flag

commit 7c9d9223802fbed4dee1ae301661bf346964c9d2 upstream.

Truncate an inode's address space when flipping the GFS2_DIF_JDATA flag:
depending on that flag, the pages in the address space will either use
buffer heads or iomap_folio_state structs, and we cannot mix the two.

Reported-by: Kun Hu &lt;huk23@m.fudan.edu.cn&gt;, Jiaji Qin <jjtan24@m.fudan.edu.cn>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>