hugetlb: use sizeof() to get the array size

It's better to use sizeof() to get the array size instead of manual
calculation. Minor readability improvement.

Link: https://lkml.kernel.org/r/20220901120030.63318-5-linmiaohe@huawei.com


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