*: use NULL for null pointers

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/e2fsprogs/old_e2fsprogs/ext2fs/ext_attr.c b/e2fsprogs/old_e2fsprogs/ext2fs/ext_attr.c
index 7ee41f2..a2ba12d 100644
--- a/e2fsprogs/old_e2fsprogs/ext2fs/ext_attr.c
+++ b/e2fsprogs/old_e2fsprogs/ext2fs/ext_attr.c
@@ -68,7 +68,7 @@
 {
 	errcode_t	retval;
 	struct ext2_ext_attr_header *header;
-	char	*buf = 0;
+	char	*buf = NULL;
 
 	if ((blk >= fs->super->s_blocks_count) ||
 	    (blk < fs->super->s_first_data_block))