MAINTAINERS: Update maintainer entry for NBD

The old maintainers email is bouncing and I've rewritten most of this
driver in the recent months.  Also add linux-block to the mailinglist
and remove the old tree, I will send patches through the linux-block
tree.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

MAINTAINERS

@@ -8599,10 +8599,10 @@ S:	Maintained
 F:	drivers/net/ethernet/netronome/
 
 NETWORK BLOCK DEVICE (NBD)
-M:	Markus Pargmann <mpa@pengutronix.de>
+M:	Josef Bacik <jbacik@fb.com>
 S:	Maintained
+L:	linux-block@vger.kernel.org
 L:	nbd-general@lists.sourceforge.net
-T:	git git://git.pengutronix.de/git/mpa/linux-nbd.git
 F:	Documentation/blockdev/nbd.txt
 F:	drivers/block/nbd.c
 F:	include/uapi/linux/nbd.h