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/build-support/testers/test-equal-derivation.nix

@@ -0,0 +1,26 @@
+{ lib, runCommand, emptyFile, nix-diff }:
+
+assertion: a: b:
+let
+  drvA = builtins.unsafeDiscardOutputDependency a.drvPath or (throw "testEqualDerivation second argument must be a package");
+  drvB = builtins.unsafeDiscardOutputDependency b.drvPath or (throw "testEqualDerivation third argument must be a package");
+  name =
+    if a?name
+    then "testEqualDerivation-${a.name}"
+    else "testEqualDerivation";
+in
+if drvA == drvB then
+  emptyFile
+else
+  runCommand name
+    {
+      inherit assertion drvA drvB;
+      nativeBuildInputs = [ nix-diff ];
+    } ''
+      echo "$assertion"
+      echo "However, the derivations differ:"
+      echo
+      echo nix-diff $drvA $drvB
+      nix-diff $drvA $drvB
+      exit 1
+    ''