AP_HAL_ChibiOS: added const for PersistentData

libraries/AP_HAL_ChibiOS/HAL_ChibiOS_Class.cpp

@@ -213,7 +213,7 @@ static void main_loop()
 
     if (hal.util->was_watchdog_reset()) {
         AP::internalerror().error(AP_InternalError::error_t::watchdog_reset);
-        AP_HAL::Util::PersistentData &pd = hal.util->persistent_data;
+        const AP_HAL::Util::PersistentData &pd = hal.util->persistent_data;
         AP::logger().Write("WDOG", "TimeUS,Task,IErr,IErrCnt,MavMsg,MavCmd,SemLine", "QbIIHHH",
                            AP_HAL::micros64(),
                            pd.scheduler_task,

libraries/AP_HAL_ChibiOS/Scheduler.cpp

@@ -350,7 +350,7 @@ void Scheduler::_monitor_thread(void *arg)
         if (loop_delay >= 200) {
             // the main loop has been stuck for at least
             // 200ms. Starting logging the main loop state
-            AP_HAL::Util::PersistentData &pd = hal.util->persistent_data;
+            const AP_HAL::Util::PersistentData &pd = hal.util->persistent_data;
             AP::logger().Write("MON", "TimeUS,LDelay,Task,IErr,IErrCnt,MavMsg,MavCmd,SemLine", "QIbIIHHH",
                                AP_HAL::micros64(),
                                loop_delay,