msm: ipc: Initialize unused elements of control message to 0

Initialize the entire control message to 0, so that unused elements of
a control message are initialized to 0. This will prevent any uninitialized
elements from leaking information to the remote subsystems.

Change-Id: I910f3956e8f282e614216c45f7af92d741d887f8
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>