The max9286 driver supports multiple output formats but only a single
one is reported through the .enum_mbus_code operation.

Fix that.
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20240617161135.130719-10-jacopo.mondi@ideasonboard.comSigned-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>