RDMA/core: Fix a WARN() message

The first parameter of WARN_ONCE() is a condition, then following
parameters are the message.  In this case, we left out the condition so it
will just print the ops->type string.

Fixes: 3856ec4b ("RDMA/core: Add RDMA_NLDEV_CMD_NEWLINK/DELLINK support")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Majd Dibbiny <majd@mellanox.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>