package/lm-sensors: fix download URL

According to http://www.lm-sensors.org/
"the previous hosting for lm-sensors.org has been discontinued and the
 former website maintainers can't be reached. For now, please refer to
 the Internet Archive of the old site until a replacement is created:
 https://web.archive.org/web/20150905145034/http://www.lm-sensors.org/"

This site points to ftp://ftp.netroedge.com/pub/lm-sensors/

 as a mirror
site for this package, so let's use it until upstream can fix its web
site.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>