V4L/DVB (5232): Gl861: correct oops when loading module

This patch moves the DVB_USB_IS_AN_I2C_ADAPTER flag from the adapter
properties to the device properties.
Without this patch I get an OOPS when the gl861 driver tries to
access any registers.

Signed-off-by: Jan Nijs <jan.nijs@scarlet.be>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>