vdpa/mlx5: set default queue indices

vdpa/mlx5: set default queue indices

The rte_vhost_get_vring_base function is being called to get the values
of last_avail_idx and last_used_idx.
These fields will not have the correct values in case the function
returns an error.

Adding a check for the function return value, and in the case of an
error, set the fields to be zero and print a warning message.

Fixes: bff735011078 ("vdpa/mlx5: prepare virtio queues")
Cc: stable@dpdk.org
Signed-off-by: Asaf Penso <asafp@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>