AC_WPNav: take references to inav's position rather than a copy

libraries/AC_WPNav/AC_WPNav.cpp

@@ -283,7 +283,7 @@ void AC_WPNav::shift_wp_origin_to_current_pos()
     }
 
     // get current and target locations
-    const Vector3f curr_pos = _inav.get_position();
+    const Vector3f &curr_pos = _inav.get_position();
     const Vector3f pos_target = _pos_control.get_pos_target();
 
     // calculate difference between current position and target
@@ -321,7 +321,7 @@ bool AC_WPNav::advance_wp_target_along_track(float dt)
     bool reached_leash_limit = false;   // true when track has reached leash limit and we need to slow down the target point
 
     // get current location
-    Vector3f curr_pos = _inav.get_position();
+    const Vector3f &curr_pos = _inav.get_position();
 
     // calculate terrain adjustments
     float terr_offset = 0.0f;
@@ -470,7 +470,7 @@ bool AC_WPNav::advance_wp_target_along_track(float dt)
 float AC_WPNav::get_wp_distance_to_destination() const
 {
     // get current location
-    Vector3f curr = _inav.get_position();
+    const Vector3f &curr = _inav.get_position();
     return norm(_destination.x-curr.x,_destination.y-curr.y);
 }
 
@@ -830,7 +830,7 @@ bool AC_WPNav::advance_spline_target_along_track(float dt)
         calculate_wp_leash_length();
 
         // get current location
-        Vector3f curr_pos = _inav.get_position();
+        const Vector3f &curr_pos = _inav.get_position();
 
         // get terrain altitude offset for origin and current position (i.e. change in terrain altitude from a position vs ekf origin)
         float terr_offset = 0.0f;