title: set_value function is not working in codeIgniter 3
body: <p>I have to set/display the value in form fields during form_validation in codeIgniter but data is not set/displaying by using set_value function. </p>
  
  <p>Here is my code,</p>
  
  <p>view page - </p>
  
  <p><strong>login_form.php</strong></p>
  
  <pre><code>&lt;?= form_open('admin/login');?&gt;
  
        &lt;?= form_label('Username','username'); ?&gt;
          &lt;?= form_input(['id'=&gt;"username", 'placeholder'=&gt;"Username", "name"=&gt;"username", 'value'=&gt;set_value('username')]); ?&gt;&lt;br&gt;
          &lt;?= form_error('username'); ?&gt;
          &lt;br&gt;
        &lt;?= form_label('Password', 'Password'); ?&gt;
          &lt;?= form_password(["id"=&gt;"password", "placeholder"=&gt;"Password", 
          "name"=&gt;"pass", "value"=&gt;set_value('pass')]); ?&gt;
          &lt;?= form_error('pass') ?&gt;
          &lt;br&gt;
          &lt;?php echo form_submit(['value'=&gt;'Login']); ?&gt;
  
  &lt;?= form_close(); ?&gt;
  </code></pre>
  
  <p>Controller - </p>
  
  <p><strong>admin.php</strong></p>
  
  <pre><code>public function login(){
  
              $this-&gt;load-&gt;library('form_validation');
              $this-&gt;form_validation-&gt;set_rules('username', 'User Name', 'required|alpha|trim');
              $this-&gt;form_validation-&gt;set_rules('pass', 'Password', 'required');
  
                  if($this-&gt;form_validation-&gt;run()):
                      echo "Validation Success";
                      else:
  
                      $this-&gt;load-&gt;view('login_form']);
  
                  endif;
          }
  </code></pre>
  
  <p>Please help and give suggestion regarding this.</p>