Ok, just another step… to be sure you did everything well.
When you download the android sdk … the installer of the 'sdk' does not install anything ! Yep… it's true.
What you need to do after, is to run the "android" manager. You found it into the /path/to/sdk/tools/android
When you run it, it appear a list of available developer packager organized on the basis of the Android version and API level you want to develop for.
Select and install some of these (like API 19, API 10).
After that, try to reopen the Qt creator and set the sdk and ndk path, now it should see that there is some kits.