Revert "usb-ccid: fix bus leak"

The bus is not owned by the device.

This reverts commit 410a096a.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20180613172815.32738-2-marcandre.lureau@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/dev-smartcard-reader.c

@@ -1147,7 +1147,6 @@ static void ccid_unrealize(USBDevice *dev, Error **errp)
     USBCCIDState *s = USB_CCID_DEV(dev);
 
     ccid_bulk_in_clear(s);
-    object_unref(OBJECT(&s->bus));
 }
 
 static void ccid_flush_pending_answers(USBCCIDState *s)