kodi: allow using patch with kodi addons

I see no reason why we shouldn't just copy from `.` rather than `$src`.
One benefit of this is that the various patch phases update the context
of `.` rather than the immutable `$src`, which means they actually have
an effect on the build derivation now.

pkgs/applications/video/kodi/build-kodi-addon.nix

@@ -13,7 +13,7 @@ toKodiAddon (stdenv.mkDerivation ({
   installPhase = ''
     runHook preInstall
 
-    cd $src/$sourceDir
+    cd ./$sourceDir
     d=$out${addonDir}/${namespace}
     mkdir -p $d
     sauce="."