net/mlx4_core: Removed unnecessary bit operation condition

Fix the "warn: suspicious bitop condition" made by the smatch semantic
checker on:
drivers/net/ethernet/mellanox/mlx4/main.c:509 mlx4_slave_cap()

Signed-off-by: Eyal Perry <eyalpe@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>