soc: qcom: spcom: fix spcom channel lock

This change adds lock while updating channel table entry. The channel
table modification must be exclusively locked for changes, because it is
accessed by many different contexts.
This change fixes uneven unlock.

Change-Id: I9bb82cb77aafbd732f7c6d3c7b2271b31d082da5
Signed-off-by: Konstantin Dorfman <kdorfman@codeaurora.org>