virtio_ring: remove the arg vq of vring_alloc_desc_extra()

The parameter vq of vring_alloc_desc_extra() is useless. This patch
removes this parameter.

Subsequent patches will call this function to avoid passing useless
arguments.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220624025621.128843-6-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>