AC_AttitudeControl: adjust for some methods on AP_AHRS become non-const

libraries/AC_AttitudeControl/AC_PosControl.cpp

@@ -189,7 +189,7 @@ const AP_Param::GroupInfo AC_PosControl::var_info[] = {
 // Note that the Vector/Matrix constructors already implicitly zero
 // their values.
 //
-AC_PosControl::AC_PosControl(const AP_AHRS_View& ahrs, const AP_InertialNav& inav,
+AC_PosControl::AC_PosControl(AP_AHRS_View& ahrs, const AP_InertialNav& inav,
                              const AP_Motors& motors, AC_AttitudeControl& attitude_control) :
     _ahrs(ahrs),
     _inav(inav),

libraries/AC_AttitudeControl/AC_PosControl.h

@@ -45,7 +45,7 @@ class AC_PosControl
 public:
 
     /// Constructor
-    AC_PosControl(const AP_AHRS_View& ahrs, const AP_InertialNav& inav,
+    AC_PosControl(AP_AHRS_View& ahrs, const AP_InertialNav& inav,
                   const AP_Motors& motors, AC_AttitudeControl& attitude_control);
 
     ///
@@ -379,7 +379,7 @@ protected:
     void check_for_ekf_z_reset();
 
     // references to inertial nav and ahrs libraries
-    const AP_AHRS_View &        _ahrs;
+    AP_AHRS_View &        _ahrs;
     const AP_InertialNav&       _inav;
     const AP_Motors&            _motors;
     AC_AttitudeControl&         _attitude_control;

libraries/AC_AttitudeControl/AC_PosControl_Sub.cpp

@@ -1,6 +1,6 @@
 #include "AC_PosControl_Sub.h"
 
-AC_PosControl_Sub::AC_PosControl_Sub(const AP_AHRS_View& ahrs, const AP_InertialNav& inav,
+AC_PosControl_Sub::AC_PosControl_Sub(AP_AHRS_View& ahrs, const AP_InertialNav& inav,
                                      const AP_Motors& motors, AC_AttitudeControl& attitude_control) :
     AC_PosControl(ahrs, inav, motors, attitude_control),
     _alt_max(0.0f),

libraries/AC_AttitudeControl/AC_PosControl_Sub.h

@@ -4,7 +4,7 @@
 
 class AC_PosControl_Sub : public AC_PosControl {
 public:
-    AC_PosControl_Sub(const AP_AHRS_View & ahrs, const AP_InertialNav& inav,
+    AC_PosControl_Sub(AP_AHRS_View & ahrs, const AP_InertialNav& inav,
                       const AP_Motors& motors, AC_AttitudeControl& attitude_control);
 
     /// set_alt_max - sets maximum altitude above the ekf origin in cm