Add unimplemented code for ControllerModifyVolume

Author: travisyx

pkg/gce-pd-csi-driver/controller.go

@@ -718,6 +718,10 @@ func (gceCS *GCEControllerServer) createSingleDisk(ctx context.Context, req *csi
 	return disk, nil
 }
 
+func (gceCS *GCEControllerServer) ControllerModifyVolume(ctx context.Context, req *csi.ControllerModifyVolumeRequest) (*csi.ControllerModifyVolumeResponse, error) {
+	return nil, status.Error(codes.Unimplemented, "ControllerModifyVolume unsupported")
+}
+
 func (gceCS *GCEControllerServer) DeleteVolume(ctx context.Context, req *csi.DeleteVolumeRequest) (*csi.DeleteVolumeResponse, error) {
 	var err error
 	// Validate arguments