auxdisplay: ht16k33: do not try to free fbdev

'fbdev' is allocated as part of larger ht16k33_priv structure; trying to
free it will cause troubles.

Acked-by: Robin van der Gracht <robin@protonic.nl>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>