MAINTAINERS: Add file patterns for rtc device tree bindings

Submitters of device tree binding documentation may forget to CC
the subsystem maintainer if this is missing.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: rtc-linux@googlegroups.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

MAINTAINERS

@@ -9558,6 +9558,7 @@ L:	rtc-linux@googlegroups.com
 Q:	http://patchwork.ozlabs.org/project/rtc-linux/list/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/abelloni/linux.git
 S:	Maintained
+F:	Documentation/devicetree/bindings/rtc/
 F:	Documentation/rtc.txt
 F:	drivers/rtc/
 F:	include/linux/rtc.h