soc: qcom: spcom: fix poll() for channel connected

Userspace loads SP application and immediately polls for link up on
spcom channel matching the application loaded.

There is a race between rpmsg device arrived and channel state becomes
connected, so poll() called on channel returns 1(link up) to spcomlib.

This change fixes link up logic: instead of checking the channel
completion state, need to check that rpmsg device arrived for the
channel.

Change-Id: I1920a9a55d6ab0cf886996b27e32515df465cc9b
Signed-off-by: Konstantin Dorfman <kdorfman@codeaurora.org>