mm/hugetlb.c: undo errant change

During conflict resolution a line was unintentionally removed by a ksm.c
patch.

Link: https://lkml.kernel.org/r/85b0d694-d1ac-8e7a-2e50-1edc03eee21a@google.com
Fixes: ac90c56b ("mm/ksm: refactor out try_to_merge_with_zero_page()")
Reported-by: Hugh Dickins <hughd@google.com>
Cc: Aristeu Rozanski <aris@redhat.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/hugetlb.c

@@ -2631,6 +2631,7 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 retry:
 	spin_unlock_irq(&hugetlb_lock);
 	for (i = 0; i < needed; i++) {
+		folio = NULL;
 		for_each_node_mask(node, cpuset_current_mems_allowed) {
 			if (!mbind_nodemask || node_isset(node, *mbind_nodemask)) {
 				folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),