[media] vp702x: rename struct vp702x_state -> vp702x_adapter_state

We need a state struct for the dvb_usb_device.
In order to reduce confusion we rename the vp702x_state struct.

Signed-off-by: Florian Mickler <florian@mickler.org>
Cc: Patrick Boettcher <pb@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>