MAINTAINERS: add backlight co-maintainers

Bryan Wu and Lee Jones volunteer to maintain backlight drivers and help
to setup git-tree for backlight subsystem.  Thus, I add them as
backlight co-maintainers.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Bryan Wu <cooloney@gmail.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>