hugetlb: use LIST_HEAD() to define a list head

Use LIST_HEAD() directly to define a list head to simplify the code.
No functional change intended.

Link: https://lkml.kernel.org/r/20220901120030.63318-4-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>