nixos/steam-hardware: add uinput to boot.kernelModules

uinput needs to be added to boot.kernelModules in order for the udev
rules defined by steam to be run and set permissions correctly on
/dev/uinput.

See https://github.com/NixOS/nixpkgs/issues/70471.

nixos/modules/hardware/steam-hardware.nix

@@ -21,5 +21,12 @@ in
     services.udev.packages = [
       pkgs.steamPackages.steam
     ];
+
+    # The uinput module needs to be loaded in order to trigger the udev rules
+    # defined in the steam package for setting permissions on /dev/uinput.
+    #
+    # If the udev rules are not triggered, some controllers won't work with
+    # steam.
+    boot.kernelModules = [ "uinput" ];
   };
 }