vdpa/mlx5: fix steering update in virtq unset

vdpa/mlx5: fix steering update in virtq unset

When a virtq is destroyed by the driver, it must be removed from the
steering RQT which holds its reference.

The driver didn't remove the virtq from RQT before destroying it what
caused HW syndrome in virtq unset.

Remove the virtq from RQT before destroying it.

Fixes: 9f09b1ca15c5 ("vdpa/mlx5: recreate a virtq becoming enabled")
Cc: stable@dpdk.org
Signed-off-by: Xueming Li <xuemingl@mellanox.com>
Signed-off-by: Matan Azrad <matan@mellanox.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>