AC_WPNav: integrate AC_PosControl::get_roll_cd rename

libraries/AC_WPNav/AC_WPNav.h

@@ -192,8 +192,8 @@ public:
     ///
 
     /// get desired roll, pitch which should be fed into stabilize controllers
-    float get_roll() const { return _pos_control.get_roll(); }
-    float get_pitch() const { return _pos_control.get_pitch(); }
+    float get_roll() const { return _pos_control.get_roll_cd(); }
+    float get_pitch() const { return _pos_control.get_pitch_cd(); }
     Vector3f get_thrust_vector() const { return _pos_control.get_thrust_vector(); }
 
     /// advance_wp_target_along_track - move target location along track from origin to destination