msm: synx: acquire ref of synx handle in each function

The change ensures appropriate reference is held in
each function before accessing valid synx handle.

This avoids release function destroying the synx
handle while any other process is working with the
same handle, leading to use-after-free issues.

Change-Id: I5b828c5ab6f7fcdd5b5a66e04d9c7c827de5d15f
Signed-off-by: Sumukh Hallymysore Ravindra <shallymy@codeaurora.org>