MAINTAINERS: Update entries for Kees Cook

Update current email address for Kees Cook in the MAINTAINER file to
match the change from commit 4e173c82 ("mailmap: update entry for
Kees Cook").

Link: https://lore.kernel.org/r/20240617181257.work.206-kees@kernel.org


Signed-off-by: Kees Cook <kees@kernel.org>