*: use NULL for null pointers

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/e2fsprogs/old_e2fsprogs/ext2fs/closefs.c b/e2fsprogs/old_e2fsprogs/ext2fs/closefs.c
index 008d5f3..7ba7f22 100644
--- a/e2fsprogs/old_e2fsprogs/ext2fs/closefs.c
+++ b/e2fsprogs/old_e2fsprogs/ext2fs/closefs.c
@@ -206,8 +206,8 @@
 	blk_t		group_block;
 	errcode_t	retval;
 	unsigned long	fs_state;
-	struct ext2_super_block *super_shadow = 0;
-	struct ext2_group_desc *group_shadow = 0;
+	struct ext2_super_block *super_shadow = NULL;
+	struct ext2_group_desc *group_shadow = NULL;
 	char	*group_ptr;
 	int	old_desc_blocks;
 #if BB_BIG_ENDIAN