Also, name the driver "brymen-bm857" in preparation to doing "subdrivers" for other Brymen models later (similar to serial-dmm).
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>