mm/page_alloc: use costly_order in WARN_ON_ONCE_GFP()

There's no need to check whether order > PAGE_ALLOC_COSTLY_ORDER again. 
Minor readability improvement.

Link: https://lkml.kernel.org/r/20220916072257.9639-15-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -5280,7 +5280,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 		 * so that we can identify them and convert them to something
 		 * else.
 		 */
-		WARN_ON_ONCE_GFP(order > PAGE_ALLOC_COSTLY_ORDER, gfp_mask);
+		WARN_ON_ONCE_GFP(costly_order, gfp_mask);
 
 		/*
 		 * Help non-failing allocations by giving them access to memory