hugetlb: pass NULL to kobj_to_hstate() if nid is unused

We can pass NULL to kobj_to_hstate() directly when nid is unused to
simplify the code. No functional change intended.

Link: https://lkml.kernel.org/r/20220901120030.63318-7-linmiaohe@huawei.comSigned-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>

mm/hugetlb.c

@@ -3763,8 +3763,7 @@ HSTATE_ATTR_WO(demote);
 static ssize_t demote_size_show(struct kobject *kobj,
 					struct kobj_attribute *attr, char *buf)
 {
-	int nid;
-	struct hstate *h = kobj_to_hstate(kobj, &nid);
+	struct hstate *h = kobj_to_hstate(kobj, NULL);
 	unsigned long demote_size = (PAGE_SIZE << h->demote_order) / SZ_1K;
 
 	return sysfs_emit(buf, "%lukB\n", demote_size);
@@ -3777,7 +3776,6 @@ static ssize_t demote_size_store(struct kobject *kobj,
 	struct hstate *h, *demote_hstate;
 	unsigned long demote_size;
 	unsigned int demote_order;
-	int nid;
 
 	demote_size = (unsigned long)memparse(buf, NULL);
 
@@ -3789,7 +3787,7 @@ static ssize_t demote_size_store(struct kobject *kobj,
 		return -EINVAL;
 
 	/* demote order must be smaller than hstate order */
-	h = kobj_to_hstate(kobj, &nid);
+	h = kobj_to_hstate(kobj, NULL);
 	if (demote_order >= h->order)
 		return -EINVAL;