ARM: at91/dt: aks-cdu: define slow crytal frequency

Define AK signal CDU slow crystal frequency

Signed-off-by: Alexandre Belloni <[e-mail]>
Acked-by: Nicolas Ferre <[e-mail]>

arch/arm/boot/dts/aks-cdu.dts

···
 		bootargs = "console=ttyS0,115200 ubi.mtd=4 root=ubi0:rootfs rootfstype=ubifs";
 	};
 
+	clocks {
+		slow_xtal {
+			clock-frequency = <32768>;
+		};
+	};
+
 	ahb {
 		apb {
 			usart0: serial@fffb0000 {