ACM-simple: don't use uninitialised simple trig values

ArduCopter/ArduCopter.pde

@@ -1419,7 +1419,7 @@ void update_roll_pitch_mode(void)
 // new radio frame is used to make sure we only call this at 50hz
 void update_simple_mode(void)
 {
-	float simple_sin_y, simple_cos_x;
+	float simple_sin_y=0, simple_cos_x=0;
 
 	// used to manage state machine
 	// which improves speed of function