soc: qcom: ipc_router_glink_xprt: Fix while handling CONNECTED event

The channel CONNECTED event may happen before the call to glink_open()
returns. Cache the channel handle under that scenario.

CRs-Fixed: 913647
Change-Id: I3777acdff3423b96cb527a826415faca11d1ed19
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>