media: omap3isp: Quit using struct v4l2_subdev.host_priv field

struct v4l2_subdev.host_priv is intended to be used by another driver. This
is hardly good design but back in the days of platform data was a quick
hack to get things done.

As the sub-device specific bus information can be stored to the ISP driver
specific struct allocated along with v4l2_async_subdev, keep the
information there and only there.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>