usb: glink: Fix crash on quick disconnect and connect

On very quick USB disconnect and connect we are trying
to open the G-Link channel before the previous session
was properly closed, resulting in a crash.
Prevent this by making sure the G-Link channel is
opened only once the previous session was closed
properly.

CRs-Fixed: 2130811
Change-Id: Id8ab16a3154a9c8e987f560f0b8a6dd0ce80a8a6
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>