USB: mos7720: delete parport

parport subsystem has introduced parport_del_port() to delete a port
when it is going away. Without parport_del_port() the registered port
will not be unregistered.
To reproduce and verify the error:
Command to be used is : ls /sys/bus/parport/devices
1) without the device attached there is no output as there is no
registered parport.
2) Attach the device, and the command will show "parport0".
3) Remove the device and the command still shows "parport0".
4) Attach the device again and we get "parport1".

With the patch applied:
1) without the device attached there is no output as there is no
registered parport.
2) Attach the device, and the command will show "parport0".
3) Remove the device and there is no output as "parport0" is now
removed.
4) Attach device again to get "parport0" again.

Cc: <stable@vger.kernel.org> # 4.2+
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/mos7720.c

@@ -2007,6 +2007,7 @@ static void mos7720_release(struct usb_serial *serial)
 				    urblist_entry)
 			usb_unlink_urb(urbtrack->urb);
 		spin_unlock_irqrestore(&mos_parport->listlock, flags);
+		parport_del_port(mos_parport->pp);
 
 		kref_put(&mos_parport->ref_count, destroy_mos_parport);
 	}