hplipWithPlugin: correct arch name for the plugin file on aarch64

[mebubo]

Motivation for this change

Without this change, building hplipWithPlugin on aarch64 fails with:

cp: cannot stat 'lj-aarch64.so': No such file or directory
builder for '/nix/store/p0x02ppv0n1xj46wvik3p3cn4jikmr1q-hplip-3.20.11.drv' failed with exit code 1

This is because the corresponding file in the archive is actually called
lj-arm64.so.

hplipPlatforms exists to convert between the different names; this
commit only changes the value to a correct one.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[r-rmcgibbo]

Result of nixpkgs-review pr 123086 at 5153e0e run on aarch64-linux 1

1 package built successfully:

• hplipWithPlugin

1 suggestion:

• warning: unused-argument

  Unused argument: coreutils.
  Near pkgs/misc/drivers/hplip/default.nix:6:9:

    |
  6 | , bash, coreutils, util-linux
    |         ^