devfreq: add devfreq maintainer entry

As devfreq is merged at mainline. Also update the maintainer entry.
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Kevin Hilman <khilman@ti.com>
Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -2169,6 +2169,13 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git
 S:	Maintained
 F:	drivers/usb/dwc3/
 
+DEVICE FREQUENCY (DEVFREQ)
+M:	MyungJoo Ham <myungjoo.ham@samsung.com>
+M:	Kyungmin Park <kyungmin.park@samsung.com>
+L:	linux-kernel@vger.kernel.org
+S:	Maintained
+F:	drivers/devfreq/
+
 DEVICE NUMBER REGISTRY
 M:	Torben Mathiasen <device@lanana.org>
 W:	http://lanana.org/docs/device-list/index.html