net/mlx4/mcg: Mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 114792 ("Missing break in switch")
Addresses-Coverity-ID: 114793 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/mcg.c

@@ -1412,6 +1412,7 @@ int mlx4_multicast_attach(struct mlx4_dev *dev, struct mlx4_qp *qp, u8 gid[16],
 	case MLX4_STEERING_MODE_A0:
 		if (prot == MLX4_PROT_ETH)
 			return 0;
+		/* fall through */
 
 	case MLX4_STEERING_MODE_B0:
 		if (prot == MLX4_PROT_ETH)
@@ -1441,6 +1442,7 @@ int mlx4_multicast_detach(struct mlx4_dev *dev, struct mlx4_qp *qp, u8 gid[16],
 	case MLX4_STEERING_MODE_A0:
 		if (prot == MLX4_PROT_ETH)
 			return 0;
+		/* fall through */
 
 	case MLX4_STEERING_MODE_B0:
 		if (prot == MLX4_PROT_ETH)