net/mlx5e: Fix global PFC counters replication

net/mlx5e: Fix global PFC counters replication

Currently when reading global PFC statistics we left the counter
iterator out of the equation and we ended up reading the same counter
over and over again.

Instead of reading the counter at index 0 on every iteration we now read
the counter at index (i).

Fixes: d526634190a6 ('net/mlx5e: Expose flow control counters to ethtool')
Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>