msm: rpc: Fix uninitialized union in rpc router close function

Initialize the rr_control_msg union to prevent the local users from
obtaining sensitive information from stack  memory in msm_rpcrouter_close
function.

CRs-Fixed: 515623
Change-Id: Ife87010eb81e8840c9b1bf5d8aeb941c90020eac
Signed-off-by: FNU Ramendra <rramendr@codeaurora.org>