fydetab/duo: fix hardware.firmware being applied

[RossComputerGuy]

Description of changes

Fixes this error:

       error: A definition for option `hardware.firmware' is not of type `list of package'. TypeError: Definition values:
       - In `/nix/store/1jcq7nbm2bj68bpa85fblak3c87a917r-source/fydetab/duo': <derivation ap6275p-firmware-2023-11-05>
       - In `/nix/store/1jcq7nbm2bj68bpa85fblak3c87a917r-source/fydetab/duo': <derivation mali-g610-firmware-2024-08-23>
       - In `/nix/store/1jcq7nbm2bj68bpa85fblak3c87a917r-source/fydetab/duo': <derivation himax-firmware-2024-11-09>

Also fixes the himax firmware, forgot to get a hash. I've also changed the graphics section of the README to clarify things more.

Things done

• Tested the changes in your own NixOS Configuration
• Tested the changes end-to-end by using your fork of nixos-hardware and
  importing it via <nixos-hardware> or Flake input