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/fetchmtn/default.nix

@@ -0,0 +1,25 @@
+# You can specify some extra mirrors and a cache DB via options
+{lib, stdenvNoCC, monotone, defaultDBMirrors ? [], cacheDB ? "./mtn-checkout.db"}:
+# dbs is a list of strings
+# each is an url for sync
+
+# selector is mtn selector, like h:org.example.branch
+#
+{name ? "mtn-checkout", dbs ? [], sha256
+, selector ? "h:" + branch, branch}:
+
+stdenvNoCC.mkDerivation {
+  builder = ./builder.sh;
+  nativeBuildInputs = [monotone];
+
+  outputHashAlgo = "sha256";
+  outputHashMode = "recursive";
+  outputHash = sha256;
+
+  dbs = defaultDBMirrors ++ dbs;
+  inherit branch cacheDB name selector;
+
+  impureEnvVars = lib.fetchers.proxyImpureEnvVars;
+
+}
+