complete t_fine_adjust getter

Author: SelfDrivingCarp

Adafruit_BME280.cpp

@@ -545,7 +545,7 @@ uint32_t Adafruit_BME280::sensorID(void) { return _sensorID; }
  *   @returns the current temperature compensation value in degrees Celcius
  */
 float Adafruit_BME280::getTemperatureAdjustment(void) {
-  return 0.0;
+  return float(((t_fine_adjust*5)>>8)/100);
 };
 
 /*!