MAINTAINERS: Fix path and add bindings to timers

As spotted by Andreas Färber, the clocksource directory path does not follow
the rule where a maintained directory must end with a '/' character.

Also, the timers devicetree bindings documentation is not mentioned in the
entry, so every submission touching the devicetree documentation misses to
Cc the maintainers of the timers.
Reported-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

MAINTAINERS

@@ -3444,7 +3444,8 @@ M:	Thomas Gleixner <tglx@linutronix.de>
 L:	linux-kernel@vger.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/core
 S:	Supported
-F:	drivers/clocksource
+F:	drivers/clocksource/
+F:	Documentation/devicetree/bindings/timer/
 
 CMPC ACPI DRIVER
 M:	Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>