AP_NavEKF3: unify singleton naming to _singleton and get_singleton()

libraries/AP_NavEKF2/AP_NavEKF2.cpp

@@ -611,7 +611,7 @@ bool NavEKF2::InitialiseFilter(void)
     _framesPerPrediction = uint8_t((EKF_TARGET_DT / (_frameTimeUsec * 1.0e-6) + 0.5));
 
     // see if we will be doing logging
-    AP_Logger *dataflash = AP_Logger::instance();
+    AP_Logger *dataflash = AP_Logger::get_singleton();
     if (dataflash != nullptr) {
         logging.enabled = dataflash->log_replay();
     }

libraries/AP_NavEKF3/AP_NavEKF3.cpp

@@ -635,7 +635,7 @@ bool NavEKF3::InitialiseFilter(void)
     if (core == nullptr) {
 
         // see if we will be doing logging
-        AP_Logger *dataflash = AP_Logger::instance();
+        AP_Logger *dataflash = AP_Logger::get_singleton();
         if (dataflash != nullptr) {
             logging.enabled = dataflash->log_replay();
         }