mm/page_alloc: remove unneeded variable base

Since commit 5d0a661d ("mm/page_alloc: use only one PCP list for
THP-sized allocations"), local variable base is just as same as order.  So
remove it.  No functional change intended.

Link: https://lkml.kernel.org/r/20230803114934.693989-1-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -538,8 +538,6 @@ static void bad_page(struct page *page, const char *reason)
 
 static inline unsigned int order_to_pindex(int migratetype, int order)
 {
-	int base = order;
-
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (order > PAGE_ALLOC_COSTLY_ORDER) {
 		VM_BUG_ON(order != pageblock_order);
@@ -549,7 +547,7 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
 	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
 #endif
 
-	return (MIGRATE_PCPTYPES * base) + migratetype;
+	return (MIGRATE_PCPTYPES * order) + migratetype;
 }
 
 static inline int pindex_to_order(unsigned int pindex)