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/filesystems/genromfs/default.nix

@@ -0,0 +1,25 @@
+{ lib, stdenv, fetchurl }:
+
+stdenv.mkDerivation rec {
+  version = "0.5.2";
+  pname = "genromfs";
+
+  src = fetchurl {
+    url = "mirror://sourceforge/romfs/genromfs/${version}/${pname}-${version}.tar.gz";
+    sha256 = "0q6rpq7cmclmb4ayfyknvzbqysxs4fy8aiahlax1sb2p6k3pzwrh";
+  };
+
+  postPatch = ''
+    substituteInPlace Makefile \
+      --replace "prefix = /usr" "prefix = $out" \
+      --replace "gcc" "cc"
+  '';
+
+  meta = with lib; {
+    homepage = "http://romfs.sourceforge.net/";
+    description = "Tool for creating romfs file system images";
+    license = licenses.gpl2;
+    maintainers = with maintainers; [ ];
+    platforms = platforms.all;
+  };
+}