jack2: fix missing alsa-lib feature dependency

jack2 needs snd_hwdep support.

Fixes:
  http://autobuild.buildroot.net/results/4c3/4c3b4f1db5c1aadfd8de59f7a655a7644f1bc1be/



Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>