AP_NavEKF3: use origin lat for earth rates

home may not yet be set when this code is run, so using home may be
invalid

libraries/AP_NavEKF3/AP_NavEKF3_Control.cpp

@@ -473,7 +473,7 @@ bool NavEKF3_core::setOriginLLH(const Location &loc)
     EKF_origin = loc;
     ekfGpsRefHgt = (double)0.01 * (double)EKF_origin.alt;
     // define Earth rotation vector in the NED navigation frame at the origin
-    calcEarthRateNED(earthRateNED, _ahrs->get_home().lat);
+    calcEarthRateNED(earthRateNED, loc.lat);
     validOrigin = true;
     return true;
 }
@@ -489,7 +489,7 @@ void NavEKF3_core::setOrigin()
     }
     ekfGpsRefHgt = (double)0.01 * (double)EKF_origin.alt;
     // define Earth rotation vector in the NED navigation frame at the origin
-    calcEarthRateNED(earthRateNED, _ahrs->get_home().lat);
+    calcEarthRateNED(earthRateNED, EKF_origin.lat);
     validOrigin = true;
     gcs().send_text(MAV_SEVERITY_INFO, "EKF3 IMU%u Origin set to GPS",(unsigned)imu_index);
 }