ARM: shmobile: bockw dts: set extal clock frequency

Sets the extal clock to the frequency of the oscillator installed by
default (33 MHz).
Signed-off-by: NUlrich Hecht <ulrich.hecht+renesas@gmail.com>
Acked-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7778-bockw.dts

@@ -61,6 +61,10 @@
 	};
 };
 
+&extal_clk {
+	clock-frequency = <33333333>;
+};
+
 &mmcif {
 	pinctrl-0 = <&mmc_pins>;
 	pinctrl-names = "default";