cpufreq: don't print value of .driver_data from core

CPUFreq core doesn't control value of .driver_data and this field is
completely driver specific. This can contain any value and not only
indexes. For most of the drivers, which aren't using this field, its
value is zero. So, printing this from core doesn't make any sense.
Don't print it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>