USB: serial: symbolserial.c: use module_usb_serial_driver
This converts the symbolserial.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: Rusty Russell <rusty@rustcorp.com.au> CC: Johan Hovold <jhovold@gmail.com> CC: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com> CC: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>