MAINTAINERS: Add file patterns for cpufreq device tree bindings

Submitters of device tree binding documentation may forget to CC
the subsystem maintainer if this is missing.
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -3450,6 +3450,7 @@ 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)
 B:	https://bugzilla.kernel.org
 F:	Documentation/cpu-freq/
+F:	Documentation/devicetree/bindings/cpufreq/
 F:	drivers/cpufreq/
 F:	include/linux/cpufreq.h
 F:	tools/testing/selftests/cpufreq/