AP_Motors: added accessors for ff output to motors

needed for tailsitters

libraries/AP_Motors/AP_Motors_Class.h

@@ -112,8 +112,11 @@ public:
 
     // accessors for roll, pitch, yaw and throttle inputs to motors
     float               get_roll() const { return _roll_in; }
+    float               get_roll_ff() const { return _roll_in_ff; }
     float               get_pitch() const { return _pitch_in; }
+    float               get_pitch_ff() const { return _pitch_in_ff; }
     float               get_yaw() const { return _yaw_in; }
+    float               get_yaw_ff() const { return _yaw_in_ff; }
     float               get_throttle_out() const { return _throttle_out; }
     float               get_throttle() const { return constrain_float(_throttle_filter.get(), 0.0f, 1.0f); }
     float               get_throttle_bidirectional() const { return constrain_float(2 * (_throttle_filter.get() - 0.5f), -1.0f, 1.0f); }