spcom: avoid using stale glink handle

spcom_notify_state() is a callback called by glink upon channel connect.
It is asynchronous callback, that might be called after glink_close().
Avoid storing stale glink handle in such case.

Change-Id: I10359f38ca48f618899673f677a6409b01bc6618
Signed-off-by: Amir Samuelov <amirs@codeaurora.org>