rpmsg: glink: Put an extra reference during cleanup

In a remote processor crash scenario, there is no guarantee the remote
processor sent close requests before it went into a bad state. Remove
the reference that is normally handled by the close command in the
so channel resources can be released.

Change-Id: I02980914bfb587990c3277a945193fb89e76c504
Signed-off-by: Chris Lew <clew@codeaurora.org>