ARM: dts: at91: at91sam9n12: witch sckc to new clock bindings

Switch slow clock controller to new clock bindings.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20230517094119.2894220-4-claudiu.beznea@microchip.com