cpufrequtils: Replace non-existant kernel.org git source

git://git.kernel.org/pub/scm/utils/kernel/cpufreq/cpufrequtils.git
no longer exists so build fails, unless it is already present in
downloads directory.

Source has been retrieved from a mirror:
(http://mirror.nexcess.net/kernel.org/scm/utils/kernel/cpufreq/cpufrequtils.git

)
and a new git source has been established on github.

kernel.org link kept in a comment to allow the old
link to be easily reestablished once it is available.

Signed-off-by: Ulf Samuelsson <ulf@emagii.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>