spcom: avoid false error message on spcom_device_release()

Typically, spcom device nodes are associated with a glink channel.
However, /dev/spcom and /dev/sp_ssr have other purposes,
and they are not associated with a channel.
Avoid error message when user call file close()
for /dev/spcom and /dev/sp_ssr.

Change-Id: I5dd55ad3c7ff93efb2e332fcab49b58cbc177c90
Signed-off-by: Amir Samuelov <amirs@codeaurora.org>