AP_Rangefinder : make get_temp const

This makes backend get_temp methods const

Co-Authored-By: Josh Henderson <69225461+hendjoshsr71@users.noreply.github.com>

libraries/AP_RangeFinder/AP_RangeFinder_Backend.h

@@ -61,7 +61,7 @@ public:
     uint32_t last_reading_ms() const { return state.last_reading_ms; }
 
     // get temperature reading in C.  returns true on success and populates temp argument
-    virtual bool get_temp(float &temp) { return false; }
+    virtual bool get_temp(float &temp) const { return false; }
 
 protected:
 

libraries/AP_RangeFinder/AP_RangeFinder_NMEA.cpp

@@ -50,7 +50,7 @@ bool AP_RangeFinder_NMEA::get_reading(uint16_t &reading_cm)
 }
 
 // get temperature reading
-bool AP_RangeFinder_NMEA::get_temp(float &temp)
+bool AP_RangeFinder_NMEA::get_temp(float &temp) const
 {
     uint32_t now_ms = AP_HAL::millis();
     if ((_temp_readtime_ms == 0) || ((now_ms - _temp_readtime_ms) > read_timeout_ms())) {

libraries/AP_RangeFinder/AP_RangeFinder_NMEA.h

@@ -45,7 +45,7 @@ private:
     bool get_reading(uint16_t &reading_cm) override;
 
     // get temperature reading in C.  returns true on success and populates temp argument
-    bool get_temp(float &temp) override;
+    bool get_temp(float &temp) const override;
 
     uint16_t read_timeout_ms() const override { return 3000; }