AP_AHRS: params always use set method

libraries/AP_AHRS/AP_AHRS_DCM.cpp

@@ -587,7 +587,7 @@ AP_AHRS_DCM::drift_correction_yaw(void)
 
     // sanity check _kp_yaw
     if (_kp_yaw < AP_AHRS_YAW_P_MIN) {
-        _kp_yaw = AP_AHRS_YAW_P_MIN;
+        _kp_yaw.set(AP_AHRS_YAW_P_MIN);
     }
 
     // update the proportional control to drag the
@@ -927,7 +927,7 @@ AP_AHRS_DCM::drift_correction(float deltat)
 
     // sanity check _kp value
     if (_kp < AP_AHRS_RP_P_MIN) {
-        _kp = AP_AHRS_RP_P_MIN;
+        _kp.set(AP_AHRS_RP_P_MIN);
     }
 
     // we now want to calculate _omega_P and _omega_I. The