cache-tree: mark istate->cache_changed on prime_cache_tree()

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/reset.c b/builtin/reset.c
index 0c56d28..234b2eb 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -84,7 +84,7 @@
 
 	if (reset_type == MIXED || reset_type == HARD) {
 		tree = parse_tree_indirect(sha1);
-		prime_cache_tree(&active_cache_tree, tree);
+		prime_cache_tree(&the_index, tree);
 	}
 
 	return 0;