net/mlx5: remove unused variable in Tx queue creation

net/mlx5: remove unused variable in Tx queue creation

When a CQ is not created by DevX, it be allocated by either DV function
or by regular Verbs function.

The CQ DV attributes variable was wrongly defined and initialized in Tx
queue creation while the CQ is created by the regular Verbs function
what remained the attributes variable unused.

Remove the unused variable.

Fixes: faf2667fe8d5 ("net/mlx5: separate DPDK from verbs Tx queue objects")
Cc: stable@dpdk.org
Signed-off-by: Michael Baum <michaelba@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>