mm: hugetlb_vmemmap: add check of CONFIG_MEMORY_HOTPLUG back

The compiler will optimize the code as much as possible if we add the
check of CONFIG_MEMORY_HOTPLUG back.

Link: https://lkml.kernel.org/r/20231205030530.3802-1-songmuchun@bytedance.com


Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>