net/mlx5: Fix counter list hardware structure

The counter list hardware structure doesn't contain a clear and
num_of_counters fields, remove them.

These wrong fields were never used by the driver hence no other driver
changes.

Fixes: a351a1b0 ("net/mlx5: Introduce bulk reading of flow counters")
Signed-off-by: Rabie Loulou <rabiel@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>