ARM: dts: imx: add required #clock-cells for fixed-clock

Per bindings of fixed-clock, #clock-cells is a required property.  Let's
add it for those fixed rate clocks.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

arch/arm/boot/dts/imx27-apf27.dts

@@ -29,6 +29,7 @@
 
 		osc26m {
 			compatible = "fsl,imx-osc26m", "fixed-clock";
+			#clock-cells = <0>;
 			clock-frequency = <0>;
 		};
 	};