fix(zyxel/nwa50ax): ensure the DTB is in the FIT

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

devices/zyxel-nwa50ax/default.nix

@@ -224,6 +224,7 @@
         tftp = {
           # 5MB is nice.
           freeSpaceBytes = 5 * 1024 * 1024;
+          appendDTB = true;
           loadAddress = lim.parseInt "0x2000000";
         };
       };