ASoC: msm: qdsp6v2: fix broken unmap memory regions

Current adm_memory_unmap_regions() does nothing since the packet size
was filled with zero.  This consequently fixes following memory map error
which was due to double memory mapping.

CRs-fixed: 491669, 487082
Change-Id: I1d1722fd5d10d1cfeb618e3329c84f4e2a71a477
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>