rpmsg: glink: spi: Cancel intent work in release

The remote may not get a chance to send a close command during reset.
Cancel any intent work in channel release to fully cleanup the channel
resources before freeing the channel structure.

Change-Id: I895f5bcc26bd1727e8a2277d2965597dae5a425b
Signed-off-by: Chris Lew <clew@codeaurora.org>
Signed-off-by: Divya Sharma <divyash@codeaurora.org>