MAINTAINERS, mailmap: update Sven Peter's email address

Update my mail address to my new @kernel.org one and also add a mailmap
entry to make sure everything gets sent there for easier filtering.

Signed-off-by: Sven Peter <sven@kernel.org>
Link: https://lore.kernel.org/r/20250528221718.45204-1-sven@kernel.org


Signed-off-by: Arnd Bergmann <arnd@arndb.de>