clk: at91: sckc: switch to parent_data/parent_hw

Switch slow clock drivers to use parent_data and parent_hw.
With this parent-child relation is described with pointers rather
than strings.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20230615093227.576102-10-claudiu.beznea@microchip.com