rt-tests: fix build dependencies

Some tests didn't list librttest in their dependencies.

Fixes:
http://autobuild.buildroot.net/results/999/9998dcf8c82989d9eba772e16ce3905b24badbfc/
http://autobuild.buildroot.net/results/b1e/b1e078591d65a3b5c9d638ad5bbb4ec8c28c38ef/



Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>