V4L/DVB (13455): go7007: Add struct v4l2_device.

This adds a struct v4l2_device to the go7007 device struct and registers
it during v4l2 initialization.  The v4l2_device registration overwrites
the go->dev device_data, which is a struct usb_interface with intfdata set
to the struct go7007.  This changes intfdata to point to the struct
v4l2_device inside struct go7007, which is what v4l2_device_register will
also set it to (and warn about non-null drvdata on register.)  Since usb
disconnect can happen any time, this intfdata should always be present.

Signed-off-by: Pete Eberlein <pete@sensoray.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>