net/virtio: fix mbuf count on Rx queue setup

net/virtio: fix mbuf count on Rx queue setup

Rx queue setup finish function may report wrong number of
allocated mbufs in case of in-order feature. Fix the
function to not ignore allocation error and count only
successfully allocated number of buffers.

Fixes: e5f456a98d3c ("net/virtio: support in-order Rx and Tx")
Cc: stable@dpdk.org
Signed-off-by: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>