msm: synx: Fix synx device closure

Replace the synx cleanup on file operation close
than the earlier flush. Usage of flush resulted
in memory use in the poll method after free in
flush operation.

Change-Id: I8a4d02a7804cef9b02ad0843e24d87dc80998375
Signed-off-by: Sumukh Hallymysore Ravindra <shallymy@codeaurora.org>