MAINTAINERS: chenhc@lemote.com -> chenhuacai@kernel.org

Use @kernel.org address as the main communications end point. Update the
corresponding M-entries and .mailmap (for git shortlog translation).

Signed-off-by: Huacai Chen <chenhuacai@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>