RDMA/device: Check that the rename is nop under the lock

Since another rename could be running in parallel it is safer to check
that the name is not changing inside the lock, where we already know the
device name will not change.

Fixes: d21943dd

 ("RDMA/core: Implement IB device rename function")
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Parav Pandit <parav@mellanox.com>