ipq806x: Fix nighthawk R7800/XR450/XR500 wan MAC

Correct the NVMEM mac-base field usage to read the wan MAC
correctly from flash.

Reference to discussion at https://github.com/openwrt/openwrt/pull/13952#issuecomment-1842749122

Fixes: d264d3a60 ("ipq806x: remove mac-address-increment")
Signed-off-by: Hannu Nyman <[email protected]>

target/linux/ipq806x/files/arch/arm/boot/dts/qcom-ipq8065-nighthawk.dtsi

@@ -427,7 +427,7 @@
 	pinctrl-0 = <&rgmii2_pins>;
 	pinctrl-names = "default";
 
-	nvmem-cells = <&macaddr_art_6>;
+	nvmem-cells = <&macaddr_art_6 0>;
 	nvmem-cell-names = "mac-address";
 
 	fixed-link {