ekf2: send airspeed data to ekf backend regardless of sign

On ground the airspeed can sometimes be slightly negative but the ekf
should still know that airspeed data is flowing regularly

src/modules/ekf2/EKF2.cpp

@@ -2076,14 +2076,19 @@ void EKF2::UpdateAirspeedSample(ekf2_timestamps_s &ekf2_timestamps)
 		if (_airspeed_validated_sub.update(&airspeed_validated)) {
 
 			if (PX4_ISFINITE(airspeed_validated.true_airspeed_m_s)
-			    && PX4_ISFINITE(airspeed_validated.calibrated_airspeed_m_s)
-			    && (airspeed_validated.calibrated_airspeed_m_s > 0.f)
 			    && (airspeed_validated.selected_airspeed_index > 0)
 			   ) {
+				const float cas2tas = 1.f;
+
+				if (PX4_ISFINITE(airspeed_validated.calibrated_airspeed_m_s)
+				    && (airspeed_validated.calibrated_airspeed_m_s > FLT_EPSILON)) {
+					cas2tas = airspeed_validated.true_airspeed_m_s / airspeed_validated.calibrated_airspeed_m_s;
+				}
+
 				airspeedSample airspeed_sample {
 					.time_us = airspeed_validated.timestamp,
 					.true_airspeed = airspeed_validated.true_airspeed_m_s,
-					.eas2tas = airspeed_validated.true_airspeed_m_s / airspeed_validated.calibrated_airspeed_m_s,
+					.eas2tas = cas2tas,
 				};
 				_ekf.setAirspeedData(airspeed_sample);
 			}