AP_OpticalFlow: minor order declaration change

non-functional change

libraries/AP_OpticalFlow/OpticalFlow.h

@@ -60,9 +60,6 @@ public:
     // last_update() - returns system time of last sensor update
     uint32_t last_update() const { return _last_update_ms; }
 
-    // parameter var info table
-    static const struct AP_Param::GroupInfo var_info[];
-
     struct OpticalFlow_state {
         uint8_t device_id;          // device id
         uint8_t  surface_quality;   // image quality (below TBD you can't trust the dx,dy values returned)
@@ -75,6 +72,9 @@ public:
         return _pos_offset;
     }
 
+    // parameter var info table
+    static const struct AP_Param::GroupInfo var_info[];
+
 private:
     AP_AHRS_NavEKF &_ahrs;
     OpticalFlow_backend *backend;