Undefined property: dashboard::$m_data

A PHP Error was encountered Severity: Notice

Message: Undefined property: Dashboard::$M_data

Filename: controllers/Dashboard.php

Line Number: 58

Backtrace:

File: C:\xampp\htdocs\website_ci\application\controllers\Dashboard.php Line: 58 Function: _error_handler

File: C:\xampp\htdocs\website_ci\index.php Line: 315 Function: require_once

controllers/Dashboard.php

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Dashboard extends CI_Controller {
public function ganti_password_aksi() {

        // form validasi
        $this->form_validation->set_rules('password_lama','Password Lama','required');
        $this->form_validation->set_rules('password_baru','Password Baru','required|min_length[8]');
        $this->form_validation->set_rules('konfirmasi_password','Konfirmasi Password Baru','required|matches[password_baru]');

        // cek validasi
        if($this->form_validation->run() != false){

         // menangkap data dari form
         $password_lama = $this->input->post('password_lama');
         $password_baru = $this->input->post('password_baru');
         $konfirmasi_password = $this->input->post('konfirmasi_password');

         // cek kesesuaian password lama dengan id pengguna yang sedang login dan password lama
         $where = array(
             'pengguna_id' => $this->session->userdata('id'),
             'pengguna_password' => md5($password_lama)
         );
         $cek = $this->m_data->cek_login('pengguna', $where)->num_rows();

         // cek kesesuaikan password lama
         if($cek > 0){

            // update data password pengguna
            $w = array(
                'pengguna_id' => $this->session->userdata('id')
            );
            $data = array(
                'pengguna_password' => md5($password_baru)
            );
            $this->m_data->update_data($where, $data, 'pengguna');

            // alihkan halaman kembali ke halaman ganti password
            redirect('dashboard/ganti_password?alert=sukses');
         }else{
             // alihkan halaman kembali ke halaman ganti password
             redirect('dashboard/ganti_password?alert=gagal');
         }

    }else{
        $this->load->view('dashboard/v_header');
        $this->load->view('dashboard/v_ganti_password');
        $this->load->view('dashboard/v_footer');
    }
  }
}
?>

models/m_data

<?php

class M_data extends CI_Model{
    function cek_login($table,$where){
        return $this->db->get_where($table,$where);
    }

    // fungsi untuk mengupdate atau mengubah data di database
    function update_data($where,$data,$table){
        $this->db->where($where);
        $this->db->update($table,$data);
    }
}

?>

Salahnya dimana ya? saya cari pertanyaan sama disini ada tapi juga belum berhasil seperti jawaban suruh lihat config/autoload.php

$autoload['libraries'] = array('database','session','form_validation');

terus apa ya yang salah?

Ini potongan line 58

$cek = $this->m_data->cek_login('pengguna', $where)->num_rows();