mm fix commmets: if SPARSEMEM, pgdata doesn't have page_ext

If SPARSEMEM, use page_ext in mem_section
if !SPARSEMEM, use page_ext in pgdata
Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmzone.h

@@ -1063,7 +1063,7 @@ struct mem_section {
 	unsigned long *pageblock_flags;
 #ifdef CONFIG_PAGE_EXTENSION
 	/*
-	 * If !SPARSEMEM, pgdat doesn't have page_ext pointer. We use
+	 * If SPARSEMEM, pgdat doesn't have page_ext pointer. We use
 	 * section. (see page_ext.h about this.)
 	 */
 	struct page_ext *page_ext;