TradHeli: BugFix to ColYaw

Credit to Jolyon Saunders for finding this bug.

libraries/AP_Motors/AP_MotorsHeli.cpp

@@ -581,7 +581,7 @@ void AP_MotorsHeli::move_swash(int16_t roll_out, int16_t pitch_out, int16_t coll
         // the feed-forward is not required when the motor is shut down and not creating torque
         // also not required if we are using external gyro
         if (motor_runup_complete() && _tail_type != AP_MOTORS_HELI_TAILTYPE_SERVO_EXTGYRO) {
-            yaw_offset = _collective_yaw_effect * abs(coll_out_scaled - _collective_mid_pwm);
+            yaw_offset = _collective_yaw_effect * abs(_collective_out - _collective_mid_pwm);
         }
     }