Use the frame interval stored in the subdev state instead of storing
a copy in the driver private structure.

Initialize the frame interval to the special case 0/0 that in the
max9286 driver represents automatic handling of frame sync.

As the frame sync mode is set at s_stream() time, we can remove it
from max9286_setup().
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20240617161135.130719-12-jacopo.mondi@ideasonboard.comSigned-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>