Using the class device pointer returned by tty_register_device() with
part 1 of the patch, attach the Gigaset drivers' "cidmode" sysfs entry
to its tty class device, where it can be found more easily by users
who do not know nor care which USB port the device is attached to.

Signed-off-by: Hansjoerg Lipp <hjlipp@web.de>
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>