Copter: autoyaw: correct units returned by look_ahead_yaw

there are other methods on the autoyaw object which make it clear that they're working in cd, and others in there that work in degrees.  This method doesn't specify cd yet returns in that unit.

Change the method and state variable to store in degrees (as our naming standards suggest)

ArduCopter/autoyaw.cpp

@@ -8,13 +8,14 @@ float Mode::AutoYaw::roi_yaw() const
     return get_bearing_cd(copter.inertial_nav.get_position_xy_cm(), roi.xy());
 }
 
+// returns a yaw in degrees, direction of vehicle travel:
 float Mode::AutoYaw::look_ahead_yaw()
 {
     const Vector3f& vel = copter.inertial_nav.get_velocity_neu_cms();
     const float speed_sq = vel.xy().length_squared();
     // Commanded Yaw to automatically look ahead.
     if (copter.position_ok() && (speed_sq > (YAW_LOOK_AHEAD_MIN_SPEED * YAW_LOOK_AHEAD_MIN_SPEED))) {
-        _look_ahead_yaw = degrees(atan2f(vel.y,vel.x))*100.0f;
+        _look_ahead_yaw = degrees(atan2f(vel.y,vel.x));
     }
     return _look_ahead_yaw;
 }
@@ -80,7 +81,7 @@ void Mode::AutoYaw::set_mode(Mode yaw_mode)
 
     case Mode::LOOK_AHEAD:
         // Commanded Yaw to automatically look ahead.
-        _look_ahead_yaw = copter.ahrs.yaw_sensor;
+        _look_ahead_yaw = copter.ahrs.yaw_sensor * 0.01;  // cdeg -> deg
         break;
 
     case Mode::RESETTOARMEDYAW:
@@ -230,7 +231,7 @@ float Mode::AutoYaw::yaw_cd()
 
     case Mode::LOOK_AHEAD:
         // Commanded Yaw to automatically look ahead.
-        _yaw_angle_cd = look_ahead_yaw();
+        _yaw_angle_cd = look_ahead_yaw() * 100.0;
         break;
 
     case Mode::RESETTOARMEDYAW:

ArduCopter/mode.h

@@ -341,7 +341,9 @@ class Mode {
         // rate_cds(): desired yaw rate in centidegrees/second:
         float rate_cds();
 
+        // returns a yaw in degrees, direction of vehicle travel:
         float look_ahead_yaw();
+
         float roi_yaw() const;
 
         // auto flight mode's yaw mode