cpufreq: cpufreq-dt: Improve debug about matching OPP

During test of new DT OPPs it's very helpful to print the matching
OPP in case of frequency change. So it will be easier to find frequency
rounding issues in the dts file.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>