Maintainers.txt: Update MdeModulePkg maintainers

Maintainers.txt: Update MdeModulePkg maintainers

As Star has some other focus, change Star from maintainer
to reviewer, Jian will be the first maintainer, and add
Hao as the second maintainer.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao Wu <hao.a.wu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Acked-by: Hao Wu <hao.a.wu@intel.com>
Acked-by: Jian J Wang <jian.j.wang@intel.com>