AP_AHRS: use const reference not pointers for locations

this makes life easier for the new AP_Mission library

Pair-Programmed-With: Brandon Jones <brnjones@gmail.com>

libraries/AP_AHRS/AP_AHRS.cpp

@@ -203,7 +203,7 @@ Vector2f AP_AHRS::groundspeed_vector(void)
 /*
   get position projected by groundspeed and heading
  */
-bool AP_AHRS::get_projected_position(struct Location *loc)
+bool AP_AHRS::get_projected_position(struct Location &loc)
 {
         if (!get_position(loc)) {
 		return false;

libraries/AP_AHRS/AP_AHRS.h

@@ -128,18 +128,18 @@ public:
     // dead-reckoning. Return true if a position is available,
     // otherwise false. This only updates the lat and lng fields
     // of the Location
-    virtual bool get_position(struct Location *loc) {
+    virtual bool get_position(struct Location &loc) {
         if (!_gps || _gps->status() <= GPS::NO_FIX) {
             return false;
         }
-        loc->lat = _gps->latitude;
-        loc->lng = _gps->longitude;
+        loc.lat = _gps->latitude;
+        loc.lng = _gps->longitude;
         return true;
     }
 
     // get our projected position, based on our GPS position plus
     // heading and ground speed
-    bool get_projected_position(struct Location *loc);
+    bool get_projected_position(struct Location &loc);
 
     // return a wind estimation vector, in m/s
     virtual Vector3f wind_estimate(void) {

libraries/AP_AHRS/AP_AHRS_DCM.cpp

@@ -765,13 +765,13 @@ float AP_AHRS_DCM::get_error_yaw(void)
 
 // return our current position estimate using
 // dead-reckoning or GPS
-bool AP_AHRS_DCM::get_position(struct Location *loc)
+bool AP_AHRS_DCM::get_position(struct Location &loc)
 {
     if (!_have_position) {
         return false;
     }
-    loc->lat = _last_lat;
-    loc->lng = _last_lng;
+    loc.lat = _last_lat;
+    loc.lng = _last_lng;
     location_offset(loc, _position_offset_north, _position_offset_east);
     return true;
 }

libraries/AP_AHRS/AP_AHRS_DCM.h

@@ -45,7 +45,7 @@ public:
     void            reset(bool recover_eulers = false);
 
     // dead-reckoning support
-    bool get_position(struct Location *loc);
+    bool get_position(struct Location &loc);
 
     // status reporting
     float           get_error_rp(void);