rpmsg: glink: spi: wakeup thread waiting on intent

Releasing the glink spi channel while a client is waiting
on intent request queue can result in use after free case.

Waking up the waiting thread before channel release.

Change-Id: I697f53e6e91b67c1ef3bc310f0a29dfd28ae7826
Signed-off-by: Deepak Kumar Singh <deesin@codeaurora.org>