mm/vmalloc.c: use "high-order" in description non 0-order pages

In many places, in the comments, we use both "higher-order" and
"high-order" to describe the non 0-order pages.  That is confusing,
because a "higher-order" statement does not reflect what it is compared
with.

Link: https://lkml.kernel.org/r/20240906095049.3486-1-urezki@gmail.com


Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Suggested-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>