ARM: at91/dt: ge863-pro3: define main crystal frequency

Define Telit GE863-PRO3 main crystal frequency.
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: NNicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/ge863-pro3.dtsi

@@ -19,6 +19,10 @@
 			compatible = "atmel,osc", "fixed-clock";
 			clock-frequency = <6000000>;
 		};
+
+		main_xtal {
+			clock-frequency = <6000000>;
+		};
 	};
 
 	ahb {