cpufreq: Fix up printing large CPU numbers and frequency values

A negative CPU number or frequency value may be printed if they are
really large (which is unlikely, though).

Signed-off-by: Joshua Yeong <joshua.yeong@starfivetech.com>
Reviewed-by: Thorsten Blum <thorsten.blum@toblux.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
[ rjw: Subject and changelog edits. ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>