libmedia: Fix for LPA audio loss issue

-LPA playback has no audio if next clip is selected and immediately
paused.
-DirectTrack write is called after pause that makes mActive true.
Due to this, start to DirectTrack fails to reach below layers as
mActive is true. Hence no audio is heard.
-Remove mActive being made true in DirectTrack write call.

Change-Id: I2faf5a41a91f077fce9cfd8e773ceebb69e55bbb