MAINTAINERS: change my mail to the kernel.org one

As I'm doing more and more work professionally, move away from my
private mail address.

Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20231219091218.2846297-1-michael@walle.cc


Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>