securemsm-kernel: Decrement the server object ref count

in mutex context

Decrement the smcinvoke server object refcount in mutex context
so that we never get an object which is being freed.

Change-Id: I524a58d68c51ef0bec39039915d3d7f88b0c60b2
Signed-off-by: Nishant Pandey <quic_nishpand@quicinc.com>