tests/intel/xe_drm_fdinfo: Fail basic_engine_utilization if no utilization data

Replace igt_require with igt_assert to enforce that num_engines is
nonzero rather than skipping the test. This ensures the test fails
explicitly if engine utilization data is missing.

Cc: Jakub Kolakowski <jakub1.kolakowski@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Lukasz Laguna <lukasz.laguna@intel.com>
Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Signed-off-by: Marcin Bernatowicz <marcin.bernatowicz@linux.intel.com>
Reviewed-by: Jakub Kolakowski <jakub1.kolakowski@intel.com>