clk: at91: sckc: Use SCKC_{TD, MD}_SLCK IDs for clk32k clocks

Use the newly introduced macros instead of raw numbers. With this the code
is a bit easier to understand.

Reviewed-by: Alexander Dahl <ada@thorsis.com>
Link: https://lore.kernel.org/r/20240826173116.3628337-3-claudiu.beznea@tuxon.dev


Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>