ASoC: wcd_cpe: Fix message queue list corruption

When clients are trying to send message while the worker thread is
processing existing messages, there is possibility that the message
queue can get corrupted. This can result into kernel crash. Fix to make
sure the message queue does not get corrupted.

CRs-fixed: 951194
Change-Id: I1eb5232d9d079ecc9d28b95737333c1198a8b20c
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>