PID: updates for new AP_Param API

libraries/PID/PID.h

@@ -21,6 +21,7 @@ public:
         const float &   initial_d = 0.0,
         const int16_t & initial_imax = 0)
     {
+		AP_Param::setup_object_defaults(this, var_info);
         _kp = initial_p;
         _ki = initial_i;
         _kd = initial_d;