nvme namespace: `volume_name_ref` missing type

[glimchb]

see

opi-api/storage/v1alpha1/frontend_nvme_pcie.proto

Line 335 in fc749d0

string volume_name_ref = 6 [(google.api.field_behavior) = REQUIRED];

according to https://google.aip.dev/122#fields-representing-another-resource

  // The shelf where the book currently sits.
  // Format is `shelves/{shelf}`.
  string shelf = 2 [(google.api.resource_reference) = {
    type: "library.googleapis.com/Shelf"
  }];