add Logo as admin toolbar item

Hi, there

So far, I've loaded the logo into the Admin Toolbar as shown in the code below with a normal img tag. Now I would like, when the customer uploads the logo for the website on the settings page, that the Logo also displayed in the admin toolbar too.

I've tried a rwmb_get_value and rwmb_meta shortcode, but it doesn't seem to work that way.
How could I do that? Is there a possible way to do this?

$admin_bar->add_menu( array(
    'id'    => 'logo',
    'class'    => 'admin-toolbar-logo',
    'title' => '<img style="margin-top:-4px; margin-left:-2px; margin-right:10px; padding:0px; height:42px;" src="Image url" alt="">', 
    'href'  => 'Home url', 
    'meta'  => array(
        'target' => '_self',
        'onclick'  => 'doThisJS()',
    ),
));

cheers,
Sash