AC_Circle: fix references to position error

libraries/AC_WPNav/AC_Circle.h

@@ -80,7 +80,7 @@ public:
     void get_closest_point_on_circle(Vector3f &result) const;
 
     /// get horizontal distance to loiter target in cm
-    float get_distance_to_target() const { return _pos_control.get_distance_to_target(); }
+    float get_distance_to_target() const { return _pos_control.get_pos_error_xy(); }
 
     /// get bearing to target in centi-degrees
     int32_t get_bearing_to_target() const { return _pos_control.get_bearing_to_target(); }