AP_Declination: fixed build of test sketch

libraries/AP_Declination/examples/AP_Declination_test/AP_Declination_test.pde

 /// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
 
 // AVR runtime
-#include <avr/io.h>
-#include <avr/eeprom.h>
-#include <avr/pgmspace.h>
-#include <math.h>
 #include <FastSerial.h>
+#include <AP_Common.h>
+#include <AP_Math.h>
 #include <AP_Declination.h>
 
 FastSerialPort(Serial, 0);
 
 void setup(void)
 {
-	float declination = AP_Declination::get_declination(43.064191, -87.997498);
-	Serial.printf("declination: %d", declination);
+	float declination;
+
+	Serial.begin(115200);
+
+    declination = AP_Declination::get_declination(43.064191, -87.997498);
+	Serial.printf("declination: %f\n", declination);
 }
 
 void loop(void)
 {
-}
\ No newline at end of file
+}