linux-firmware: fix build, add explicit revision

pkgs/os-specific/linux/firmware/linux-firmware/default.nix

···
   version = source.version;
 
   src = fetchzip {
-    url = "https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/snapshot/linux-firmware-${version}.tar.gz";
+    url = "https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/snapshot/linux-firmware-${source.revision}.tar.gz";
     hash = source.sourceHash;
   };
 

pkgs/os-specific/linux/firmware/linux-firmware/source.nix

···
 # This file is autogenerated! Run ./update.sh to regenerate.
 {
   version = "unstable-2023-07-24";
+  revision = "59fbffa9ec8e4b0b31d2d13e715cf6580ad0e99c";
   sourceHash = "sha256-WyO/+fxQljfo6OXLC8/BomGmKtUQaJ1Lt9V5Fdv172g=";
   outputHash = "sha256-wHWPSyqxP+MGmerbc2v/hclFFJ7qKCDsupK5GASjp8s=";
 }

pkgs/os-specific/linux/firmware/linux-firmware/update.sh

···
 
 # step 1: figure out the latest version from the tags
 if [ -z "${1:-}" ]; then
-  version="$(git ls-remote --refs --tags --sort refname "$repo" | tail -n1 | cut -f2 | cut -d '/' -f3)"
+  revision="$(git ls-remote --refs --tags --sort refname "$repo" | tail -n1 | cut -f2 | cut -d '/' -f3)"
+  version=$revision
 else
-  version=$1
+  revision=$1
+  if [ -z "${2:-}" ]; then
+    version="unstable-$(date "+%Y-%m-%d")"
+  else
+    version=$2
+  fi
 fi
 
 # step 2: prefetch the source tarball
-snapshotUrl="$repo/snapshot/linux-firmware-$version.tar.gz"
+snapshotUrl="$repo/snapshot/linux-firmware-$revision.tar.gz"
 hash="$(nix-prefetch-url --unpack "$snapshotUrl")"
 sriHash="$(nix --experimental-features nix-command hash to-sri "sha256:$hash")"
 
···
 cat > source.nix << EOF
 {
   version = "$version";
+  revision = "$revision";
   sourceHash = "$sriHash";
   outputHash = null;
 }
···
 # This file is autogenerated! Run ./update.sh to regenerate.
 {
   version = "$version";
+  revision = "$revision";
   sourceHash = "$sriHash";
   outputHash = "$outHash";
 }