AP_RTC: Add missing const in member functions

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

libraries/AP_RTC/AP_RTC.cpp

@@ -90,7 +90,7 @@ bool AP_RTC::get_utc_usec(uint64_t &usec) const
     return true;
 }
 
-bool AP_RTC::get_system_clock_utc(uint8_t &hour, uint8_t &min, uint8_t &sec, uint16_t &ms)
+bool AP_RTC::get_system_clock_utc(uint8_t &hour, uint8_t &min, uint8_t &sec, uint16_t &ms) const
 {
      // get time of day in ms
     uint64_t time_ms = 0;
@@ -113,7 +113,7 @@ bool AP_RTC::get_system_clock_utc(uint8_t &hour, uint8_t &min, uint8_t &sec, uin
     return true;
 }
 
-bool AP_RTC::get_local_time(uint8_t &hour, uint8_t &min, uint8_t &sec, uint16_t &ms)
+bool AP_RTC::get_local_time(uint8_t &hour, uint8_t &min, uint8_t &sec, uint16_t &ms) const
 {
      // get local time of day in ms
     uint64_t time_ms = 0;

libraries/AP_RTC/AP_RTC.h

@@ -38,9 +38,9 @@ public:
     /*
       get time in UTC hours, minutes, seconds and milliseconds
      */
-    bool get_system_clock_utc(uint8_t &hour, uint8_t &min, uint8_t &sec, uint16_t &ms);
+    bool get_system_clock_utc(uint8_t &hour, uint8_t &min, uint8_t &sec, uint16_t &ms) const;
     
-    bool get_local_time(uint8_t &hour, uint8_t &min, uint8_t &sec, uint16_t &ms);
+    bool get_local_time(uint8_t &hour, uint8_t &min, uint8_t &sec, uint16_t &ms) const;
 
     uint32_t get_time_utc(int32_t hour, int32_t min, int32_t sec, int32_t ms);