AC_WPNav: set_loiter_target uses set_xy_target

Loiter is only a horizontal position controller so it should not set the
z-axis position.
Moved pos_control.set_speed and accel functions so order matches
init_loiter_targets function order

libraries/AC_WPNav/AC_WPNav.cpp

@@ -125,19 +125,17 @@ void AC_WPNav::set_loiter_target(const Vector3f& position, bool reset_I)
     // initialise position controller
     _pos_control.init_xy_controller();
 
+    // initialise pos controller speed and acceleration
+    _pos_control.set_speed_xy(_loiter_speed_cms);
+    _loiter_accel_cms = _loiter_speed_cms/2.0f;
+    _pos_control.set_accel_xy(_loiter_accel_cms);
+
     // set target position
-    _pos_control.set_pos_target(position);
+    _pos_control.set_xy_target(position.x, position.y);
 
     // initialise feed forward velocity to zero
     _pos_control.set_desired_velocity(0,0);
 
-    // initialise pos controller speed
-    _pos_control.set_speed_xy(_loiter_speed_cms);
-
-    // initialise pos controller acceleration
-    _loiter_accel_cms = _loiter_speed_cms/2.0f;
-    _pos_control.set_accel_xy(_loiter_accel_cms);
-
     // initialise desired accel and add fake wind
     _loiter_desired_accel.x = 0;
     _loiter_desired_accel.y = 0;