package/luvi: needs git submodules

package/luvi: needs git submodules

Luvi bundles several libraries previously provided by the upstream
tarball. Since the tarball is not available anymore we need to fetch
the git submodules. Unbundling is very hard, and we anyway don't have
the bundled libraries in Buildroot.

Fixes
http://autobuild.buildroot.net/results/26d/26d04350a761d362f40e7bd1ac09b639d61de91a/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Acked-by: "Jörg Krause <joerg.krause@embedded.rocks>"
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>