MAINTAINERS: Add Daniel as maintainer for CLOCKSOURCE and CLOCKEVENT Drivers

I've been doing a bad job at managing the drivers/clocksource directory,
so Daniel has been helping with review and patch queuing for the clocksource
and clockevent drivers, so add him formally to the MAINTAINERS list.

Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Joe Perches <joe@perches.com>
Cc: Arnd Bergmann <arnd.bergmann@linaro.org>
Cc: Olof Johansson <olof@lixom.net>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>