soc: qcom: glink: Destroy transport's transmit workqueue

When the transport unregisters from the core, destroy the associated
transmit workqueue.

Change-Id: I3ca9dddcb46f5bdd0243bee71913df1518f293d3
Signed-off-by: Atish Kumar Patra <apatra@codeaurora.org>
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>