MAINTAINERS: Add entry for LED devices documentation

When given patches that only touch documentation directory for LED
devices (Documentation/leds/), get_maintainer doesn't list mailing list
for LED subsystem. However, the patch should be seen on that list in order
to be applied.

Add the entry for Documentation/leds/.

Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230319084604.19749-1-bagasdotme@gmail.com