*: use NULL for null pointers

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/e2fsprogs/old_e2fsprogs/ext2fs/dirblock.c b/e2fsprogs/old_e2fsprogs/ext2fs/dirblock.c
index 5d3f6a1..f651338 100644
--- a/e2fsprogs/old_e2fsprogs/ext2fs/dirblock.c
+++ b/e2fsprogs/old_e2fsprogs/ext2fs/dirblock.c
@@ -80,7 +80,7 @@
 	int		do_swap = 0;
 	errcode_t	retval;
 	char		*p, *end;
-	char		*buf = 0;
+	char		*buf = NULL;
 	struct ext2_dir_entry *dirent;
 
 	if ((fs->flags & EXT2_FLAG_SWAP_BYTES) ||