[PATCH] mm: fix a comment

[Yinan Zhang <zhangyinan2019@xxxxxxxxxxxxxxxx>]

I have noticed that the previous macro is #ifndef CONFIG_SPARSEMEM.
I think the comment of #else should be CONFIG_SPARSEMEM.

Signed-off-by: Yinan Zhang <zhangyinan2019@xxxxxxxxxxxxxxxx>
---
 mm/page_ext.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_ext.c b/mm/page_ext.c
index dfb91653d..106079e67 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -201,7 +201,7 @@ void __init page_ext_init_flatmem(void)
 	panic("Out of memory");
 }
 
-#else /* CONFIG_FLATMEM */
+#else /* CONFIG_SPARSEMEM */
 
 struct page_ext *lookup_page_ext(const struct page *page)
 {
-- 
2.23.0