net/mlx5e: TX, Fix consumer index of error cqe dump

The completion queue consumer index increments upon a call to
mlx5_cqwq_pop().
When dumping an error CQE, the index is already incremented.
Decrease one for the print command.

Fixes: 16cc14d8

 ("net/mlx5e: Dump xmit error completions")
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>