validate: Fix compiler warning about implicit enum type conversion

validate: Fix compiler warning about implicit enum type conversion

gst-validate-reporter.c:119:39: error: implicit conversion from enumeration type
      'GstValidateReportingDetails' to different enumeration type
      'GstValidateInterceptionReturn' [-Werror,-Wenum-conversion]
  GstValidateInterceptionReturn ret = GST_VALIDATE_SHOW_UNKNOWN;
                                ~~~   ^~~~~~~~~~~~~~~~~~~~~~~~~
gst-validate-reporter.c:124:11: error: implicit conversion from enumeration type
      'GstValidateReportingDetails' to different enumeration type
      'GstValidateInterceptionReturn' [-Werror,-Wenum-conversion]
    ret = iface->get_reporting_level (reporter);
        ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
gst-validate-reporter.c:127:10: error: implicit conversion from enumeration type
      'GstValidateInterceptionReturn' to different enumeration type
      'GstValidateReportingDetails' [-Werror,-Wenum-conversion]
  return ret;
  ~~~~~~ ^~~