free perf counters in driver destructor

this prevents drivers that probe on one bus then instantiate on
another from leaving behind stale/duplicate perf counters

src/drivers/airspeed/airspeed.cpp

@@ -106,6 +106,11 @@ Airspeed::~Airspeed()
 	/* free any existing reports */
 	if (_reports != nullptr)
 		delete[] _reports;
+
+	// free perf counters
+	perf_free(_sample_perf);
+	perf_free(_comms_errors);
+	perf_free(_buffer_overflows);
 }
 
 int

src/drivers/hmc5883/hmc5883.cpp

@@ -359,6 +359,11 @@ HMC5883::~HMC5883()
 	/* free any existing reports */
 	if (_reports != nullptr)
 		delete[] _reports;
+
+	// free perf counters
+	perf_free(_sample_perf);
+	perf_free(_comms_errors);
+	perf_free(_buffer_overflows);
 }
 
 int

src/drivers/ms5611/ms5611.cpp

@@ -225,6 +225,12 @@ MS5611::~MS5611()
 	if (_reports != nullptr)
 		delete[] _reports;
 
+	// free perf counters
+	perf_free(_sample_perf);
+	perf_free(_measure_perf);
+	perf_free(_comms_errors);
+	perf_free(_buffer_overflows);
+
 	delete _interface;
 }