devices/zyxel-nwa50ax: use our own more advanced DTB

OpenWRT had a DTB for the NWA50AX LEDs that I didn't pick up.

Anyway, we need to include our own special DTB for the NWA platform in general
to support A/B operations, because OpenWRT original one just mark everything else read-only.

Signed-off-by: Raito Bezarius <masterancpp@gmail.com>

devices/zyxel-nwa50ax/default.nix

@@ -147,8 +147,11 @@
         rootDevice = "ubi:rootfs";
 
         dts = {
-          src = "${openwrt.src}/target/linux/ramips/dts/mt7621_zyxel_nwa50ax.dts";
+          # Actually, this is not what we want.
+          # This DTS is insufficient.
+          src = ./mt7621_zyxel_nwa50ax.dtsi;
           includes = [
+            "${./.}"
             "${openwrt.src}/target/linux/ramips/dts"
           ];
         };