Fix "Pubsub Subscription Different Project" example

PR GoogleCloudPlatform#2342 changed this example from using `id` to `name`, which removed the project ID from the topic. However, the point of this example is to show how to set up a cross-project subscription, so the example no longer works. This change reverts that change from PR GoogleCloudPlatform#2342.

Fixes hashicorp/terraform-provider-google#11642.
Fixes hashicorp/terraform-provider-google#6024.

mmv1/templates/terraform/examples/pubsub_subscription_different_project.tf.erb

@@ -6,5 +6,5 @@ resource "google_pubsub_topic" "<%= ctx[:primary_resource_id] %>" {
 resource "google_pubsub_subscription" "<%= ctx[:primary_resource_id] %>" {
   project = "<%= ctx[:vars]['subscription_project'] %>"
   name    = "<%= ctx[:vars]['subscription_name'] %>"
-  topic   = google_pubsub_topic.<%= ctx[:primary_resource_id] %>.name
+  topic   = google_pubsub_topic.<%= ctx[:primary_resource_id] %>.id
 }