ASoC: msm-cpe-lsm: Fix out of memory on buffer allocation

The buffer used for look-ahead-buffering is allocated during IOCTL from
userspace. It is possible that userspace can invoke this IOCTL multiple
times without invoking the IOCTL to de-allocate the buffer. This results
in out of memory issue for buffer allocation during stress testing. Fix
this issue by avoiding multiple buffer allocations.

CRs-fixed: 942452
Change-Id: Id9eb99dc2c8527fbbe1fe79fca1cdcea232c33da
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>