arm64: dts: imx8mq-librem5: add missing #clock-cells

'#clock-cells' is a dependency of 'clock-output-names', following
binding doc, add it.
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mq-librem5.dtsi

@@ -830,6 +830,7 @@ pmic: pmic@4b {
 		pinctrl-names = "default";
 		pinctrl-0 = <&pinctrl_pmic>, <&pinctrl_camera_pwr>;
 		clocks = <&pmic_osc>;
+		#clock-cells = <0>;
 		clock-names = "osc";
 		clock-output-names = "pmic_clk";
 		interrupt-parent = <&gpio1>;