RDMA/mlx4: Remove bogus dev_base_lock usage

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.com
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>