StateMachine: Add missing const in member functions

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

src/Vehicle/StateMachine.cc

@@ -51,7 +51,7 @@ void StateMachine::statesCompleted(void) const
 
 }
 
-StateMachine::StateFn StateMachine::currentState(void)
+StateMachine::StateFn StateMachine::currentState(void) const
 {
     if (_active) {
         return rgStates()[_stateIndex];

src/Vehicle/StateMachine.h

@@ -29,7 +29,7 @@ public:
     /// Move the state machine to the specified state and call the state function
     void move(StateFn stateFn);
 
-    StateFn currentState(void);
+    StateFn currentState(void) const;
 
     /// @return The number of states in the rgStates array
     virtual int stateCount(void) const = 0;