spcom: increment channel reference count after successful glink_open()

spcom_open() should increment the ref count only after successful glink
open the channel.
Otherwise, the following attempts to open the channel will fail.
glink_open() failure was noticed after SP reset (SSR), when attempting
to open the channel before the link between SP and HLOS is up.

Change-Id: I8be28ce810f54cc3fa95d14c7244921acf7edaa7
Signed-off-by: Amir Samuelov <amirs@codeaurora.org>