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: I64b07f44b66fe6793bc80bc99a09fd0521342531
Signed-off-by: Shaik Jabida <quic_sjabida@quicinc.com>
(cherry picked from commit 14c551f6abb3ad841accc8af91c4a18c0a78b2fe)