Keeping the character's speed the same

So I'm trying to create a Dota or LoL type movement(which I am oh so very far from doing) and aquired the click to move script from the wiki. I noticed that the farther I click from the character, the faster he will move to it. I want to keep it the same speed no matter how far the mouse's position is. How do I do this? Here's the script:

 // Click To Move script
 
 // Moves the object towards the mouse position on left mouse click
 
 
 
 var smooth:int; // Determines how quickly object moves towards position
 
 
 
 private var targetPosition:Vector3;
 
 var marker : GameObject;
 
 private var mousePos : Vector3;
 
 private var worldPos : Vector3;
 
 var User : GameObject;
 
 
 
 function Update () {
 
      var controller : CharacterController = GetComponent(CharacterController);
 
     if(Input.GetKeyDown(KeyCode.Mouse1))
 
     {         
 
         var playerPlane = new Plane(Vector3.up, transform.position);
 
         var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
 
         var hitdist = 0.0f;
 
         
 
         if (playerPlane.Raycast (ray, hitdist)) {
 
             var targetPoint = ray.GetPoint(hitdist);
 
             targetPosition = ray.GetPoint(hitdist);
 
             var targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
 
             transform.rotation = targetRotation;   
         }
  
        if(Input.GetMouseButton(1)) {
 
         mousePos = Input.mousePosition;
 
         mousePos.z = 1;
 
         var cloneMarker = Instantiate(marker,worldPos,Quaternion.identity);
 
         Destroy(cloneMarker, .5f);
 
         }
   
         Debug.DrawLine(User.transform.position, targetPosition, Color.red);
       
 
     }
 
     transform.position = Vector3.Lerp (transform.position, targetPosition, Time.deltaTime * smooth);
 
 }
  
 @script RequireComponent(CharacterController)
   

So, what can i do? Thanks for help!