MAINTAINERS: Add selftests/timers to the timekeeping maintainance list

Since I'm adding a bunch of tests to selftests/timers, put me
on the hook in the maintainers file.

Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Tested-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

MAINTAINERS

@@ -8542,6 +8542,7 @@ F:	include/uapi/linux/timex.h
 F:	kernel/time/clocksource.c
 F:	kernel/time/time*.c
 F:	kernel/time/ntp.c
+F:	tools/testing/selftests/timers/
 
 SC1200 WDT DRIVER
 M:	Zwane Mwaikambo <zwanem@gmail.com>