AP_ADC_AnalogSource: fix for new AnalogIn interface

libraries/AP_ADC_AnalogSource/AP_ADC_AnalogSource.cpp

@@ -1,12 +1,22 @@
 
 #include "AP_ADC_AnalogSource.h"
 
-float AP_ADC_AnalogSource::read() {
+/* Unfortunately we don't have a valid implementaton for read_latest - we
+ * only have access to the average from the ADC driver. Not really a big deal
+ * in our application currently. */
+
+float AP_ADC_AnalogSource::read_latest() {
+    return read_average();
+}
+
+float AP_ADC_AnalogSource::read_average() {
     float fullscale = _adc->Ch(_ch);
     float scaled = _prescale * fullscale;
     return scaled;
 }
 
+
+
 void AP_ADC_AnalogSource::set_pin(uint8_t machtnichts) {
     /* it would be an error to call this
      * but for now we'll leave it a no-op. */

libraries/AP_ADC_AnalogSource/AP_ADC_AnalogSource.h

@@ -11,7 +11,8 @@ public:
     AP_ADC_AnalogSource( AP_ADC * adc, uint8_t ch, float prescale = 1.0 ) :
         _adc(adc), _ch(ch), _prescale(prescale)
     {}
-    float           read(void);
+    float           read_average(void);
+    float           read_latest(void);
     void            set_pin(uint8_t);
 
 private: