arm64: dts: imx8mq-phanbell: make dts use gpio-fan matrix instead of array

No functional changes.

Adjust to comply with dt-schema requirements
and make possible to validate values.
Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mq-phanbell.dts

@@ -39,7 +39,7 @@ reg_usdhc2_vmmc: regulator-usdhc2-vmmc {
 
 	fan: gpio-fan {
 		compatible = "gpio-fan";
-		gpio-fan,speed-map = <0 0 8600 1>;
+		gpio-fan,speed-map = <0 0>, <8600 1>;
 		gpios = <&gpio3 5 GPIO_ACTIVE_HIGH>;
 		#cooling-cells = <2>;
 		pinctrl-names = "default";