media: mtk_mdp_m2m: Access v4l2_fh from file

media: mtk_mdp_m2m: Access v4l2_fh from file

The v4l2_fh associated with an open file handle is now guaranteed
to be available in file->private_data, initialised by v4l2_fh_add().

Access the v4l2_fh, and from there the driver-specific structure,
from the file * in all ioctl handlers.

Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Co-developed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>