mc_pos_control: fix derivative spike when regaining velocity estimate

When having no velocity estimate the derivative was updated with zero.
When losing the velocity estimate this is fine since the resulting
derivative spike doesn't get used and acceleration is set to NAN.
But when regaining the velocity estimate the spike from zero to
the first estimated velocity gets used as acceleration in the position
controller and results in a twitch.

To solve this I use the derivative reset I introduced in pr #13522
commit b64abf48b2

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -456,10 +456,9 @@ MulticopterPositionControl::set_vehicle_states(const float &vel_sp_z)
 	} else {
 		_states.velocity(0) = _states.velocity(1) = NAN;
 		_states.acceleration(0) = _states.acceleration(1) = NAN;
-
-		// since no valid velocity, update derivate with 0
-		_vel_x_deriv.update(0.0f);
-		_vel_y_deriv.update(0.0f);
+		// reset derivatives to prevent acceleration spikes when regaining velocity
+		_vel_x_deriv.reset();
+		_vel_y_deriv.reset();
 	}
 
 	if (PX4_ISFINITE(_local_pos.vz) && _local_pos.v_z_valid) {
@@ -476,9 +475,8 @@ MulticopterPositionControl::set_vehicle_states(const float &vel_sp_z)
 
 	} else {
 		_states.velocity(2) = _states.acceleration(2) = NAN;
-		// since no valid velocity, update derivate with 0
-		_vel_z_deriv.update(0.0f);
-
+		// reset derivative to prevent acceleration spikes when regaining velocity
+		_vel_z_deriv.reset();
 	}
 }