serial/JSM: change maintainer to myself

Lucas has moved on. Since his email address does not work any more, it's
not expected to get his ack.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>