MAINTAINERS: update list for NBD

nbd-general@sourceforge.net becomes nbd@other.debian.org, because
sourceforge is just a spamtrap these days.

Signed-off-by: Wouter Verhelst <w@uter.be>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

MAINTAINERS

@@ -9348,7 +9348,7 @@ NETWORK BLOCK DEVICE (NBD)
 M:	Josef Bacik <jbacik@fb.com>
 S:	Maintained
 L:	linux-block@vger.kernel.org
-L:	nbd-general@lists.sourceforge.net
+L:	nbd@other.debian.org
 F:	Documentation/blockdev/nbd.txt
 F:	drivers/block/nbd.c
 F:	include/uapi/linux/nbd.h