mm: teach mincore_hugetlb about pte markers

By checking huge_pte_none(), we incorrectly classify PTE markers as
"present".  Instead, check huge_pte_none_mostly(), classifying PTE markers
the same as if the PTE were completely blank.

PTE markers, unlike other kinds of swap entries, don't reference any
physical page and don't indicate that a physical page was mapped
previously.  As such, treat them as non-present for the sake of mincore().

Link: https://lkml.kernel.org/r/20230302222404.175303-1-jthoughton@google.com
Fixes: 5c041f5d

 ("mm: teach core mm about pte markers")
Signed-off-by: James Houghton <jthoughton@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>