ASoc: msm: Fix for pcm_read getting struck in alsa core.

Advance hardware pointer by period size even if the packet
size is 0. QDSP6 sometimes(for rapid device switches) gives
0 size packets and this results in elapsed_timeout in pcm core.

CRs-fixed: 578738
Change-Id: I7d6451b93a3447535250c0bbfe7cad7157dcd7ac
Signed-off-by: Anish Kumar <kanish@codeaurora.org>
Signed-off-by: Damir Didjusto <damird@codeaurora.org>