media: staging: most: Store v4l2_fh pointer in file->private_data

media: staging: most: Store v4l2_fh pointer in file->private_data

Most V4L2 drivers store the v4l2_fh pointer in file->private_data. The
most driver instead stores the pointer to the driver-specific structure
that embeds the v4l2_fh. Switch to storing the v4l2_fh pointer itself to
standardize behaviour across drivers. This also prepares for future
refactoring that depends on v4l2_fh being stored in private_data.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>