AP_Scheduler: Add missing const in member functions

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

libraries/AP_Scheduler/AP_Scheduler.cpp

@@ -256,7 +256,7 @@ void AP_Scheduler::run(uint32_t time_available)
 /*
   return number of micros until the current task reaches its deadline
  */
-uint16_t AP_Scheduler::time_available_usec(void)
+uint16_t AP_Scheduler::time_available_usec(void) const
 {
     uint32_t dt = AP_HAL::micros() - _task_time_started;
     if (dt > _task_time_allowed) {

libraries/AP_Scheduler/AP_Scheduler.h

@@ -108,7 +108,7 @@ public:
     void run(uint32_t time_available);
 
     // return the number of microseconds available for the current task
-    uint16_t time_available_usec(void);
+    uint16_t time_available_usec(void) const;
 
     // return debug parameter
     uint8_t debug_flags(void) { return _debug; }

libraries/AP_Scheduler/PerfInfo.cpp

@@ -160,7 +160,7 @@ float AP::PerfInfo::get_filtered_time() const
     return filtered_loop_time;
 }
 
-void AP::PerfInfo::update_logging()
+void AP::PerfInfo::update_logging() const
 {
     gcs().send_text(MAV_SEVERITY_WARNING,
                     "PERF: %u/%u [%lu:%lu] F=%uHz sd=%lu Ex=%lu",

libraries/AP_Scheduler/PerfInfo.h

@@ -34,7 +34,7 @@ public:
     float    get_filtered_time() const;
     void set_loop_rate(uint16_t rate_hz);
 
-    void update_logging();
+    void update_logging() const;
 
     // allocate the array of task statistics for use by @SYS/tasks.txt
     void allocate_task_info(uint8_t num_tasks);