AP_NavEKF2: fix writeOptFlowMeas signature

const some of the vectors, stop taking references to scalars that aren't
being changed

libraries/AP_NavEKF2/AP_NavEKF2.cpp

@@ -1082,7 +1082,7 @@ bool NavEKF2::use_compass(void) const
 // The sign convention is that a RH physical rotation of the sensor about an axis produces both a positive flow and gyro rate
 // msecFlowMeas is the scheduler time in msec when the optical flow data was received from the sensor.
 // posOffset is the XYZ flow sensor position in the body frame in m
-void NavEKF2::writeOptFlowMeas(uint8_t &rawFlowQuality, Vector2f &rawFlowRates, Vector2f &rawGyroRates, uint32_t &msecFlowMeas, const Vector3f &posOffset)
+void NavEKF2::writeOptFlowMeas(const uint8_t rawFlowQuality, const Vector2f &rawFlowRates, const Vector2f &rawGyroRates, const uint32_t msecFlowMeas, const Vector3f &posOffset)
 {
     if (core) {
         for (uint8_t i=0; i<num_cores; i++) {

libraries/AP_NavEKF2/AP_NavEKF2.h

@@ -212,7 +212,7 @@ public:
     // The sign convention is that a RH physical rotation of the sensor about an axis produces both a positive flow and gyro rate
     // msecFlowMeas is the scheduler time in msec when the optical flow data was received from the sensor.
     // posOffset is the XYZ flow sensor position in the body frame in m
-    void  writeOptFlowMeas(uint8_t &rawFlowQuality, Vector2f &rawFlowRates, Vector2f &rawGyroRates, uint32_t &msecFlowMeas, const Vector3f &posOffset);
+    void  writeOptFlowMeas(const uint8_t rawFlowQuality, const Vector2f &rawFlowRates, const Vector2f &rawGyroRates, const uint32_t msecFlowMeas, const Vector3f &posOffset);
 
     // return data for debugging optical flow fusion for the specified instance
     // An out of range instance (eg -1) returns data for the the primary instance

libraries/AP_NavEKF2/AP_NavEKF2_Measurements.cpp

@@ -117,7 +117,7 @@ void NavEKF2_core::readRangeFinder(void)
 
 // write the raw optical flow measurements
 // this needs to be called externally.
-void NavEKF2_core::writeOptFlowMeas(uint8_t &rawFlowQuality, Vector2f &rawFlowRates, Vector2f &rawGyroRates, uint32_t &msecFlowMeas, const Vector3f &posOffset)
+void NavEKF2_core::writeOptFlowMeas(const uint8_t rawFlowQuality, const Vector2f &rawFlowRates, const Vector2f &rawGyroRates, const uint32_t msecFlowMeas, const Vector3f &posOffset)
 {
     // The raw measurements need to be optical flow rates in radians/second averaged across the time since the last update
     // The PX4Flow sensor outputs flow rates with the following axis and sign conventions:

libraries/AP_NavEKF2/AP_NavEKF2_core.h

@@ -198,7 +198,7 @@ public:
     // The sign convention is that a RH physical rotation of the sensor about an axis produces both a positive flow and gyro rate
     // msecFlowMeas is the scheduler time in msec when the optical flow data was received from the sensor.
     // posOffset is the XYZ flow sensor position in the body frame in m
-    void  writeOptFlowMeas(uint8_t &rawFlowQuality, Vector2f &rawFlowRates, Vector2f &rawGyroRates, uint32_t &msecFlowMeas, const Vector3f &posOffset);
+    void  writeOptFlowMeas(const uint8_t rawFlowQuality, const Vector2f &rawFlowRates, const Vector2f &rawGyroRates, const uint32_t msecFlowMeas, const Vector3f &posOffset);
 
     // return data for debugging optical flow fusion
     void getFlowDebug(float &varFlow, float &gndOffset, float &flowInnovX, float &flowInnovY, float &auxInnov, float &HAGL, float &rngInnov, float &range, float &gndOffsetErr) const;