audioflinger: Increase Client heap size

This increase is needed to accommodate higher sampling rate clip
playback over devices like BT and to support gapless playback with
larger buffer sizes. In both cases, the cblk memory allocated for a track
can be high enough that a new allocation (either due to restoreTrack_l or
opening a new track) can fail.

Change-Id: I96f674706184f029259802d5552f5ceeebc689c1
CRs-Fixed: 768106