V4L/DVB: s2255drv: cleanup of device structure

s2255drv: cleanup of device structure

cleanup of device structure.
single channel array instead of multiple arrays in device for
each channel property.
simplifies open callback by removing search for channel index.

Signed-off-by: Dean Anderson <linux-dev@sensoray.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>