MAINTAINERS: Add bug tracking system location entry for cpufreq

The kernel Bugzilla is used for tracking cpufreq bugs, so document
that.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Len Brown <len.brown@intel.com>

MAINTAINERS

@@ -3336,6 +3336,7 @@ 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)
+B:	https://bugzilla.kernel.org
 F:	Documentation/cpu-freq/
 F:	drivers/cpufreq/
 F:	include/linux/cpufreq.h