hal: align fragment size to 24 instead of 1024 for PCM offload

Aligning PCM buffer size to 1024 bytes is not required in case
of PCM offloading. It actually creates problem when playing
6 ch, 96KHz, 16-bit stream PCM in offload mode, due to aligning
PCM data becomes unequal for the six channels.
Align the buffer to LCM of 2, 4, 6, 8 i.e. 24.

Change-Id: I0823ca2ccdd5fceaf23a182b763a1d69f91f602f
CRs-fixed: 780001