uboot: (firmwareOdroidC2/C4) don't invoke patch tool, use patches = [] instead

https://github.com/NixOS/nixpkgs/blob/master/pkgs/stdenv/generic/setup.sh#L948
this can do it nicely.

Signed-off-by: Anton Arapov <anton@deadbeef.mx>

pkgs/tools/misc/fbcat/default.nix

@@ -0,0 +1,36 @@
+{ lib
+, stdenv
+, fetchFromGitHub
+, netpbm
+}:
+
+stdenv.mkDerivation rec {
+  pname = "fbcat";
+  version = "0.5.2";
+
+  src = fetchFromGitHub {
+    owner = "jwilk";
+    repo = pname;
+    rev = version;
+    sha256 = "sha256-ORzcd8XGy2BfwuPK5UX+K5Z+FYkb+tdg/gHl3zHjvbk=";
+  };
+
+  postPatch = ''
+    substituteInPlace fbgrab \
+      --replace 'pnmtopng' '${netpbm}/bin/pnmtopng' \
+      --replace 'fbcat' "$out/bin/fbcat"
+  '';
+
+  installFlags = [
+    "PREFIX=${placeholder "out"}"
+  ];
+
+  meta = with lib; {
+    homepage = "http://jwilk.net/software/fbcat";
+    description = "Framebuffer screenshot tool";
+    license = licenses.gpl2Plus;
+    maintainers = [ maintainers.matthiasbeyer ];
+    platforms = platforms.linux;
+  };
+}
+