AP_NavEKF3: pin P references in non-writing files to const

Change their define so they don't use the mutable original, only the
name through a const-cast pointer. There are no writes to the covariance
matrix in these files, so nothing else needs changing.

libraries/AP_NavEKF3/AP_NavEKF3_AirDataFusion.cpp

@@ -4,7 +4,7 @@
 #include "AP_NavEKF3_core.h"
 #include <AP_DAL/AP_DAL.h>
 
-#define P (Pmut)
+#define P (const_cast<const Matrix24 &>(Pmut))
 
 /********************************************************
 *                   RESET FUNCTIONS                     *

libraries/AP_NavEKF3/AP_NavEKF3_Logging.cpp

@@ -12,7 +12,7 @@
 
 #pragma GCC diagnostic ignored "-Wnarrowing"
 
-#define P (Pmut)
+#define P (const_cast<const Matrix24 &>(Pmut))
 
 void NavEKF3_core::Log_Write_XKF1(uint64_t time_us) const
 {

libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp

@@ -8,7 +8,7 @@
 #include <AP_DAL/AP_DAL.h>
 #include <AP_InternalError/AP_InternalError.h>
 
-#define P (Pmut)
+#define P (const_cast<const Matrix24 &>(Pmut))
 
 #if AP_RANGEFINDER_ENABLED
 /********************************************************

libraries/AP_NavEKF3/AP_NavEKF3_OptFlowFusion.cpp

@@ -9,7 +9,7 @@
 #include <GCS_MAVLink/GCS.h>
 #include <AP_DAL/AP_DAL.h>
 
-#define P (Pmut)
+#define P (const_cast<const Matrix24 &>(Pmut))
 
 /********************************************************
 *                   RESET FUNCTIONS                     *

libraries/AP_NavEKF3/AP_NavEKF3_Outputs.cpp

@@ -5,7 +5,7 @@
 #include <AP_DAL/AP_DAL.h>
 #include <GCS_MAVLink/GCS.h>
 
-#define P (Pmut)
+#define P (const_cast<const Matrix24 &>(Pmut))
 
 // Check basic filter health metrics and return a consolidated health status
 bool NavEKF3_core::healthy(void) const

libraries/AP_NavEKF3/AP_NavEKF3_RngBcnFusion.cpp

@@ -5,7 +5,7 @@
 
 #include <AP_DAL/AP_DAL.h>
 
-#define P (Pmut)
+#define P (const_cast<const Matrix24 &>(Pmut))
 
 // initialise state:
 void NavEKF3_core::BeaconFusion::InitialiseVariables()