[android] Ensure src/ dir is present in build-generic
Some binary factory builds fail because the src/ folder is not present.
While I'm having trouble reproducing it locally I have a good theory why it is happening. The src folder was always created during the build-kde-dependencies step, but since I fixed the dependency skipping in the android-kf5-sdk container for some apps there are no dependencies built any more and the folder never gets created. By ensuring src/ is created before cloning the repo this should be fixed