MAINTAINERS: update f2fs entry

This patch includes below modifications:
1. change my maintainership from reviewer to maintainer.
2. remove maintainership of Changman Lee since he is not active about
one and a half year.
3. change website of f2fs from wiki to kernel one.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>