epkowa: fix parsing of interpreters (#82909)

Building with -std=c99 breaks the obsolete "%as" format string, which
completely breaks the parsing of epkowa interpreters. This means that
no scanner requiring plugins worked.

pkgs/misc/drivers/epkowa/default.nix

@@ -244,6 +244,7 @@ stdenv.mkDerivation rec {
       sha256 = "04y70qjd220dpyh771fiq50lha16pms98mfigwjczdfmx6kpj1jd";
     })
     ./firmware_location.patch
+    ./sscanf.patch
     ];
   patchFlags = [ "-p0" ];