diff: convert fill_filespec to struct object_id

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/diff.c b/builtin/diff.c
index 8c03dda..b2d7c32 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -57,8 +57,8 @@ static void stuff_change(struct diff_options *opt,
 
 	one = alloc_filespec(old_name);
 	two = alloc_filespec(new_name);
-	fill_filespec(one, old_oid->hash, old_oid_valid, old_mode);
-	fill_filespec(two, new_oid->hash, new_oid_valid, new_mode);
+	fill_filespec(one, old_oid, old_oid_valid, old_mode);
+	fill_filespec(two, new_oid, new_oid_valid, new_mode);
 
 	diff_queue(&diff_queued_diff, one, two);
 }