MAINTAINERS: Add RTC subsystem repository

The RTC subsystem patches are available through my kernel.org repository.
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

MAINTAINERS

@@ -8245,6 +8245,7 @@ M:	Alessandro Zummo <a.zummo@towertech.it>
 M:	Alexandre Belloni <alexandre.belloni@free-electrons.com>
 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/rtc.txt
 F:	drivers/rtc/