ASoC: msm: qdsp6v2: Fix crash while unmap in NT mode encoders.

On non tunnel mode enconding stability runs there is a crash in unmap
regions. There is an invalid access to the buffer node after it is
freed. Fix is to come out of the list once buffer node is freed.

CRs-Fixed: 470017
Change-Id: Ic699da7b85e62746ce22322f6bede5382435bcab
Signed-off-by: Krishnankutty Kolathappilly <kkolat@codeaurora.org>