mm: page_alloc: use the correct type of list for free pages

Commit bf75f200 ("mm/page_alloc: add page->buddy_list and
page->pcp_list") introduces page->buddy_list and page->pcp_list as a union
with page->lru, but missed to change get_page_from_free_area() to use
page->buddy_list to clarify the correct type of list for a free page.

Link: https://lkml.kernel.org/r/7e7ab533247d40c0ea0373c18a6a48e5667f9e10.1687333557.git.baolin.wang@linux.alibaba.comSigned-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -727,7 +727,7 @@ static inline struct page *get_page_from_free_area(struct free_area *area,
 					    int migratetype)
 {
 	return list_first_entry_or_null(&area->free_list[migratetype],
-					struct page, lru);
+					struct page, buddy_list);
 }
 
 /*