USB: serial: opticon: hook up suspend/resume callbacks

With a previous patch, the usb_driver suspend/resume callbacks got
overridden and were never called if a usb_serial driver defined them.
This patch fixes the opticon driver to move the suspend/resume callbacks
into the usb_serial_driver structure where they will be properly called.

It then removes the unused usb_driver structure.

Cc: Johan Hovold <jhovold@gmail.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Cc: Julia Lawall <julia@diku.dk>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>