RDMA/mlx4: Remove bogus dev_base_lock usage

It is not clear what this lock protects. If the authors wanted to ensure
that "dev" does not disappear, that is impossible, given the following
code path:

mlx4_ib_netdev_event (under RTNL mutex)
-> mlx4_ib_scan_netdevs
   -> mlx4_ib_update_qps

Also, the dev_base_lock does not protect dev->dev_addr either.

So it serves no purpose here. Remove it.

Link: https://lore.kernel.org/r/20201208193928.1500893-1-vladimir.oltean@nxp.comReviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/mlx4/main.c

@@ -2265,10 +2265,7 @@ static void mlx4_ib_update_qps(struct mlx4_ib_dev *ibdev,
 	u64 release_mac = MLX4_IB_INVALID_MAC;
 	struct mlx4_ib_qp *qp;
 
-	read_lock(&dev_base_lock);
 	new_smac = mlx4_mac_to_u64(dev->dev_addr);
-	read_unlock(&dev_base_lock);
-
 	atomic64_set(&ibdev->iboe.mac[port - 1], new_smac);
 
 	/* no need for update QP1 and mac registration in non-SRIOV */