cmsdk: fix visible check in hasChanged

Previously the visible check was comparing the newly set value to
itself. Now we cache the old value, set new value, and can do a proper
comparison.

RM-290

Change-Id: Idbe921bfe9e311551d6bfbad432c647c129f376e
Signed-off-by: Roman Birg <roman@cyngn.com>