tty: do not check tty_unregister_driver's return value

tty: do not check tty_unregister_driver's return value

These drivers check tty_unregister_driver return value. But they don't
handle a failure correctly (they free the driver in any case). So stop
checking tty_unregister_driver return value and remove also the prints.

In the next patch, tty_unregister_driver's return type will be switched
to void.

Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: linux-xtensa@linux-xtensa.org
Cc: Jiri Kosina <jikos@kernel.org>
Cc: David Sterba <dsterba@suse.com>
Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
Acked-by: David Sterba <dsterba@suse.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210302062214.29627-34-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>