The ip_range_pods and ip_range_services map to the ip_allocation_policy cluster_secondary_range_name and cluster_secondary_range_name attributes of the google_container_cluster resource as can be seen in the module source:

resource "google_container_cluster" "zonal_primary" {
  # ...

  ip_allocation_policy {
    cluster_secondary_range_name  = "${var.ip_range_pods}"
    services_secondary_range_name = "${var.ip_range_services}"
  }
}

These need to be existing ranges in a subnetwork such as created by the google_compute_subnetwork resource:

resource "google_compute_subnetwork" "network-with-private-secondary-ip-ranges" {
  name          = "test-subnetwork"
  ip_cidr_range = "10.2.0.0/16"
  region        = "us-central1"
  network       = "${google_compute_network.custom-test.self_link}"
  secondary_ip_range {
    range_name    = "tf-test-secondary-range-update1"
    ip_cidr_range = "192.168.10.0/24"
  }
}

resource "google_compute_network" "custom-test" {
  name                    = "test-network"
  auto_create_subnetworks = false
}