AP_AHRS: NavEKF: make set_origin and get_origin WARN_IF_UNUSED as base class

libraries/AP_AHRS/AP_AHRS_NavEKF.h

@@ -151,10 +151,10 @@ public:
     // set the EKF's origin location in 10e7 degrees.  This should only
     // be called when the EKF has no absolute position reference (i.e. GPS)
     // from which to decide the origin on its own
-    bool set_origin(const Location &loc) override;
+    bool set_origin(const Location &loc) override WARN_IF_UNUSED;
 
     // returns the inertial navigation origin in lat/lon/alt
-    bool get_origin(Location &ret) const override;
+    bool get_origin(Location &ret) const override WARN_IF_UNUSED;
 
     bool have_inertial_nav() const override;