Also, consistently use 'ch' for channel variables. This matches how we
consistently use sdi, devc, and so on all over the code-base.
This fixes parts of bug #259.
This patch might also work for a number of other Brymen models
-- 859(a), 867, 869---
including their respective rebadges from Greenlee, Extech, and Amprobe.
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>