mm: cma: simplify cma_maxchunk_get()

The function opencodes for_each_clear_bitrange().  Fix that and drop most
of housekeeping code.

Link: https://lkml.kernel.org/r/20250719205401.399475-3-yury.norov@gmail.com


Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>