net/mlx5: fix -Wtype-limits compilation warnings

The commit b9a7ba55 ("net/mlx5: Use event mask based on device
capabilities") introduced a few compilation warnings due to it bumps
MLX5_EVENT_TYPE_MAX from 0x27 to 0x100 which is always greater than
an "struct {mlx5_eqe|mlx5_nb}.type" that is an "u8".

drivers/net/ethernet/mellanox/mlx5/core/eq.c: In function
'mlx5_eq_notifier_register':
drivers/net/ethernet/mellanox/mlx5/core/eq.c:948:21: warning: comparison
is always false due to limited range of data type [-Wtype-limits]
  if (nb->event_type >= MLX5_EVENT_TYPE_MAX)
                     ^~
drivers/net/ethernet/mellanox/mlx5/core/eq.c: In function
'mlx5_eq_notifier_unregister':
drivers/net/ethernet/mellanox/mlx5/core/eq.c:959:21: warning: comparison
is always false due to limited range of data type [-Wtype-limits]
  if (nb->event_type >= MLX5_EVENT_TYPE_MAX)

Fix them by removing unnecessary checkings.

Fixes: b9a7ba55 ("net/mlx5: Use event mask based on device capabilities")
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>