rpmsg: glink: cancel the intent_work during cleanup

In some cases channel intent work is getting scheduled after
channel release and accessing stale pointer.

cancel the queued channel intent work before channel clean up.

Change-Id: I5a1c175867d9bd4deb33a0bdd74d4699af4f5cf9
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>