msm: synx: remove synx client handling based on pid

Change removes the pid info stored for each client along with
redundant searching of current client session based on pid.
Instead, current client session info already stored in private
data is used.

Change-Id: I61d3cc27539a6f0efbcf364ec463c4b8093dbbe7
Signed-off-by: Sumukh Hallymysore Ravindra <shallymy@codeaurora.org>