ASoC: msm-lsm-client: Fix issue with buffer de-allocation

It is possible that LSM_STOP can be performed to stop the detection of
keyword and without completely re-opening the device, LSM_START is
performed. In this case, the look-ahead buffer should not be de-allocated
as this buffer is session specific. Fix the issue of no detection after
stop and start by making sure the LAB (Look-Ahead Buffering) buffer is
not de-allocated during LSM_STOP.

Change-Id: I6adb06549b18197e1c8f73a4323fd162b24570d7
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>
Signed-off-by: Vidyakumar Athota <vathota@codeaurora.org>