mfd: Update MAINTAINERS patterns for WM831x

The WM831x PMICs added a backlight driver and a new include directory.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

MAINTAINERS

@@ -5681,7 +5681,9 @@ F:	drivers/mfd/wm8*.c
 F:	drivers/power/wm83*.c
 F:	drivers/rtc/rtc-wm83*.c
 F:	drivers/regulator/wm8*.c
+F:	drivers/video/backlight/wm83*_bl.c
 F:	drivers/watchdog/wm83*_wdt.c
+F:	include/linux/mfd/wm831x/
 F:	include/linux/mfd/wm8350/
 F:	include/linux/mfd/wm8400/
 F:	sound/soc/codecs/wm8350.c