MAINTAINERS/serial: Change maintainer of jsm driver

Gabriel will no longer maintain this driver, so I'm adding
myself as maintainer.

Thanks for all your work on jsm driver Gabriel.
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Acked-by: Gabriel Krisman Bertazi <gabriel@krisman.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -7136,7 +7136,7 @@ S:	Maintained
 F:	drivers/media/platform/rcar_jpu.c
 
 JSM Neo PCI based serial card
-M:	Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>
+M:	Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
 L:	linux-serial@vger.kernel.org
 S:	Maintained
 F:	drivers/tty/serial/jsm/