AP_WindVane: add modern devices rev p cal

libraries/AP_WindVane/AP_WindVane_ModernDevice.cpp

@@ -52,3 +52,10 @@ void AP_WindVane_ModernDevice::update_speed()
     // simplified equation from data sheet, converted from mph to m/s
     speed_update_frontend(24.254896f * powf((analog_voltage / powf(temp_ambient, 0.115157f)), 3.009364f));
 }
+
+void AP_WindVane_ModernDevice::calibrate()
+{
+    gcs().send_text(MAV_SEVERITY_INFO, "WindVane: rev P. zero wind voltage offset set to %.1f",double(_current_analog_voltage));
+    _frontend._speed_sensor_voltage_offset.set_and_save(_current_analog_voltage);
+    _frontend._calibration.set_and_save(0);
+}