ARM: at91/dt: evk-pro3: define slow crytal frequency

Define Telit EVK-PRO3 slow crystal frequency
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: NNicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/evk-pro3.dts

@@ -15,6 +15,12 @@
 	model = "Telit EVK-PRO3 for Telit GE863-PRO3";
 	compatible = "telit,evk-pro3", "atmel,at91sam9260", "atmel,at91sam9";
 
+	clocks {
+		slow_xtal {
+			clock-frequency = <32768>;
+		};
+	};
+
 	ahb {
 		apb {
 			macb0: ethernet@fffc4000 {