net/mlx5: fix send queue doorbell

net/mlx5: fix send queue doorbell

As part of SQ creation for Tx queue objects, a HW doorbell memory should
be allocated and mapped to the HW.

The SQ doorbell handler was wrongly saved on the CQ fields what caused
wrong doorbell release in the Tx queue object destroy flow.

Save the SQ doorbell handler in the SQ fields.

Fixes: 3a87b964edd3 ("net/mlx5: create Tx queues with DevX")
Cc: stable@dpdk.org
Signed-off-by: Michael Baum <michaelba@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>