rtc: isl1208: Make similar I2C and DT-based matching table

The isl1208_id[].driver_data could store a pointer to the config,
like for DT-based matching, making I2C and DT-based matching
more similar.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230623140948.384762-8-biju.das.jz@bp.renesas.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>