AP_InertialNav: Address peer review comments

The decision to set the origin to zero has been moved out of the AHRS library and into the inertial nav library as this is consumer specific.

libraries/AP_InertialNav/AP_InertialNav_NavEKF.cpp

@@ -54,7 +54,10 @@ nav_filter_status AP_InertialNav_NavEKF::get_filter_status() const
 struct Location AP_InertialNav_NavEKF::get_origin() const
 {
     struct Location ret;
-    ret = _ahrs_ekf.get_origin();
+     if (!_ahrs_ekf.get_origin(ret)) {
+         // initialise location to all zeros if EKF1 origin not yet set
+         memset(&ret, 0, sizeof(ret));
+     }
     return ret;
 }