dsp: q6lsm: Check size of payload before access

check size of payload before access in q6lsm_mmapcallback.

The payload size can be either 4 or 8 bytes.
Code to verify the payload size is atleast 4 bytes is added.

Change-Id: I595a529829ac4d8743b604f90cb1c742a75b9e7b
Signed-off-by: Shaik Jabida <quic_sjabida@quicinc.com>
(cherry picked from commit 9b8172010c3f6ffbf1e89a6e846f8c715027cfaa)