soc: qcom: glink_smd_xprt: Plug information leaks

The close and close ack commands sent over the wire in the control channel
have reserved fields, which are left uninitialized.  This leads to an
unintentional information leak.

Zero initialize these reserved fields before sending the commands over the
wire to plug the leak.

Change-Id: I533a1bd2a7946a17e76806f6c589ea00a993c6e9
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>