ASoC: wcd_cpe_services: Clear internal state before notifying clients

When CPE services notifies the client that response to any message is
received, it is possible that the client may send another message even
before the CPE services cleared the current message response as these
both are run in different thread contexts, this will cause the command
queue to be corrupted. Fix this issue by clearing internal state of CPE
services command queue before notifying clients the clients the result
of message transfer completion.

CRs-fixed: 946375
Change-Id: I4b31201747edd7fdee57294ff559ccb21e582608
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>