Revert "AP_Airspeed: coverity scan - variables not initialized in constructor"

This reverts commit 93462d0fe3.

libraries/AP_Airspeed/AP_Airspeed.h

@@ -181,7 +181,7 @@ private:
 
     Airspeed_Calibration _calibration;
     float _last_saved_ratio;
-    uint8_t _counter = 0;
+    uint8_t _counter;
 
     float get_pressure(void);
     void update_calibration(float raw_pressure);