tty: MAINTAINERS: add drivers/serial/jsm/ as maintained driver

Soott Kilau is handing off the maintainership of the jsm serial
driver to me, and this patch just add the driver as maintained.

Signed-off-by: Breno Leitao <leitao@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>