pve-edk2-firmware: fix upstream submodule broken

[5aaee9]

Upstream subhook repo is gone. Repalced with tianocore fork.

Links:

tianocore/edk2#6398
NixOS/nixpkgs#353800

[heywoodlh]

When attempting to run this PR, I ran into this:

       error: hash mismatch in fixed-output derivation '/nix/store/c606r53i02yna84m5ds3q2mglzshd4pw-novnc-pve.drv':
         specified: sha256-BQm4hDC7b+YaFipVonzcwVG/4JswkMSFZEpVkCdfrjM=
            got:    sha256-5pybuOkvNVcP+In03ZokNpqgmGwB4DQEO4jmefV7W9Y=

Looks like this was recently taken care of in a different commit: b3f3158

@5aaee9 could this please be rebased off of current main? :)

EDIT: I have a fork that is based off latest main with this commit until this gets resolved for anyone who wants to use in the meantime: https://github.com/heywoodlh/proxmox-nixos/

[5aaee9]

@heywoodlh Rebased with main

[JulienMalka]

I don't like how hacky this is, but given that proxmox has not yet updated their edk2 mirror and this breaks our repo, will merge this until a better solution is found.

Thanks @5aaee9, @codgician :)