pvNVIDIAIndeX: fix `clang-tidy` `modernize-use-equals-default` lints

Plugins/pvNVIDIAIndeX/src/vtknvindex_affinity.cxx

Plugins/pvNVIDIAIndeX/src/vtknvindex_colormap_utility.cxx

Plugins/pvNVIDIAIndeX/src/vtknvindex_config_settings.cxx

Plugins/pvNVIDIAIndeX/src/vtknvindex_host_properties.cxx

...vNVIDIAIndeX/src/vtknvindex_irregular_volume_importer.cxx

.../pvNVIDIAIndeX/src/vtknvindex_irregular_volume_mapper.cxx

Plugins/pvNVIDIAIndeX/src/vtknvindex_opengl_canvas.cxx

Plugins/pvNVIDIAIndeX/src/vtknvindex_performance_values.cxx

Plugins/pvNVIDIAIndeX/src/vtknvindex_receiving_logger.cxx

...vNVIDIAIndeX/src/vtknvindex_regular_volume_properties.cxx

Plugins/pvNVIDIAIndeX/src/vtknvindex_representation.cxx

Plugins/pvNVIDIAIndeX/src/vtknvindex_volumemapper.cxx