Fix forcing media stream control on tablet

There's option volume_keys_control_ring_stream (Volume keys control ringtone
volume / If on, volume keys control ringtone volume. If off, volume keys
control media volume.) in Settings which is also available on tablets but it
doesn't work on these devices (I didn't find reported issue).
As I like this option and think it may be even more wanted on media devices
such as tablets, here's a fix.

Change-Id: Ib4fd2e578df5d2bd6f69626863dca20cb014c96f