Fixes: 1f23816 ("virtio_blk: add discard and write zeroes support")

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Reviewed-by: Christoph Hellwig <hch@lst.de>

Cc: Changpeng Liu <changpeng.liu@intel.com>

Cc: Daniel Verkamp <dverkamp@chromium.org>

Cc: Michael S. Tsirkin <mst@redhat.com>

Cc: Stefan Hajnoczi <stefanha@redhat.com>

Cc: Stefano Garzarella <sgarzare@redhat.com>

Signed-off-by: Jens Axboe <axboe@kernel.dk>