AP_HAL: fixed printf example build

libraries/AP_HAL/examples/Printf/Printf.pde

@@ -25,6 +25,8 @@
 #include <AP_Airspeed.h>
 #include <AP_Vehicle.h>
 #include <AP_ADC_AnalogSource.h>
+#include <AP_NavEKF.h>
+#include <AP_Rally.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;