nbd: use bd_set_size when updating disk size

nbd: use bd_set_size when updating disk size

commit 9e2b19675d1338d2a38e99194756f2db44a081df upstream.

When we stopped relying on the bdev everywhere I broke updating the
block device size on the fly, which ceph relies on.  We can't just do
set_capacity, we also have to do bd_set_size so things like parted will
notice the device size change.

Fixes: 29eaadc ("nbd: stop using the bdev everywhere")
cc: stable@vger.kernel.org
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>