MAINTAINERS: Change maintainer for hisilicon DRM driver

Remove Rongrong Zou and change tiantao as hisilicon DRM maintainer.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: xinliang.liu <xinliang.liu@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1597134186-58423-1-git-send-email-tiantao6@hisilicon.com