MAINTAINERS: Add Documentation/cpu-freq/

I am told the cpufreq documentation updates should go to the PM list.
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -3281,6 +3281,7 @@ L:	linux-pm@vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git
 T:	git git://git.linaro.org/people/vireshk/linux.git (For ARM Updates)
+F:	Documentation/cpu-freq/
 F:	drivers/cpufreq/
 F:	include/linux/cpufreq.h