net/mlx5e: Fix CQ moderation mode not set properly

cq_period_mode assignment was mistakenly removed so it was always set to "0",
which is EQE based moderation, regardless of the device CAPs and
requested value in ethtool.

Fixes: 6a9764ef ("net/mlx5e: Isolate open_channels from priv->params")
Signed-off-by: Tal Gilboa <talgi@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>