MAINTAINERS: Add wpan patchwork

This patchwork instance is hosted on kernel.org and has been used for a
long time already, it was just not mentioned in MAINTAINERS.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20230411090122.419761-2-miquel.raynal@bootlin.com
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

Author: miquelraynal

MAINTAINERS

@@ -9890,6 +9890,7 @@ M:	Miquel Raynal <miquel.raynal@bootlin.com>
 L:	linux-wpan@vger.kernel.org
 S:	Maintained
 W:	https://linux-wpan.org/
+Q:	https://patchwork.kernel.org/project/linux-wpan/list/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/wpan/wpan.git
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/wpan/wpan-next.git
 F:	Documentation/networking/ieee802154.rst