media: usb: uvcvideo: Store v4l2_fh pointer in file->private_data

media: usb: uvcvideo: Store v4l2_fh pointer in file->private_data

Most V4L2 drivers store the v4l2_fh pointer in file->private_data. The
uvcvideo 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>