Previously I had made the struct device point to the input device, but
after talking with Dmitry, he said that the USB device would make more
sense for this driver to point to.  So converted it to use that instead.

CC: Alessandro Rubini <rubini@ipvvis.unipv.it>
CC: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>