m68k/mm: use correct bit number in _PAGE_SWP_EXCLUSIVE comment

As noticed by Geert, commit b5c88f21 ("microblaze/mm: support
__HAVE_ARCH_PTE_SWP_EXCLUSIVE") modified m68k code by accident.  While
replacing 0x080 by CF_PAGE_NOCACHE is correct, although it should have
been part of commit ed415406 ("m68k/mm: support
__HAVE_ARCH_PTE_SWP_EXCLUSIVE"), replacing "bit 7" by "bit 24" in the
comment was wrong.

Let's revert to the previous, correct, comment.

Link: https://lkml.kernel.org/r/20230404085636.121409-1-david@redhat.com


Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>