f2fs: make __f2fs_write_data_pages() static

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index d34e4a0..3ba8393 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2070,7 +2070,7 @@
 	return ret;
 }
 
-int __f2fs_write_data_pages(struct address_space *mapping,
+static int __f2fs_write_data_pages(struct address_space *mapping,
 						struct writeback_control *wbc,
 						enum iostat_type io_type)
 {