Placeholders are layed wrong, they need to be in single array. Use

     $sql = "INSERT INTO {customers} (first_name,last_name,email_addr,password)
             VALUES(:fName, :lName, :email , :cpwd)";
    db_query($sql,
        array(
          ':fName' => $form_state['values']['fName'],
          ':lName' => $form_state['values']['lName'],
          ':email' => $form_state['values']['email'],
          ':cpwd' => $form_state['values']['cpwd'],
       ),
    );