vringh: reset kiov 'consumed' field in __vringh_iov()

__vringh_iov() overwrites the contents of riov and wiov, in fact it
resets the 'i' and 'used' fields, but also the 'consumed' field should
be reset to avoid an inconsistent state.

Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20210315163450.254396-4-sgarzare@redhat.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>