fix code error with array count in cariable which does not expect instance key

ohpc-instance/main.tf

@@ -72,7 +72,7 @@ resource "openstack_compute_volume_attach_v2" "volume_attach" {
 }
 
 output "xdmod_instance_id" {
-  value = openstack_compute_instance_v2.ohpc[0].id
+  value = openstack_compute_instance_v2.ohpc.id
 }
 
 output "ssh_host" {