USB: serial: io_ti.c: use module_usb_serial_driver

This converts the io_ti.c driver to use the module_usb_serial_driver() call
instead of having to have a module_init/module_exit function, saving a lot
of duplicated code.

CC: Johan Hovold <jhovold@gmail.com>
CC: Lucas De Marchi <lucas.demarchi@profusion.mobi>
CC: "Eric W. Biederman" <ebiederm@xmission.com>
CC: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>