net/mlx5: Fix length of async_event_mask

According to PRM async_event_mask have to be 64 bits long.

Signed-off-by: Eugenia Emantayev <eugenia@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>