dts: arm: nordic: Add default rtc1 clock frequency to nrf53 network core

Adds the default 32.768KHz clock frequency to this peripheral, as it is
used as the system timing source

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

Author: nordicjm

dts/arm/nordic/nrf5340_cpunet.dtsi

@@ -243,6 +243,7 @@
 			reg = <0x41016000 0x1000>;
 			cc-num = <4>;
 			interrupts = <22 NRF_DEFAULT_IRQ_PRIORITY>;
+			clock-frequency = <32768>;
 			status = "disabled";
 		};