soc: qcom: glink: Fix channel migration on fully open channel

If process_open_event is delayed and glink has migrated to new transport,
process open event will be treated as a new open event and migration will
happen on fully open channel.

If channel is fully, open migration will not be allowed as client might
already be using the channel for communication.

Change-Id: I6c1760bc19f52e7d0c1c9834a72e2304f0ae28c8
Signed-off-by: Dhoat Harpal <hdhoat@codeaurora.org>