RDMA/NLDEV: remove mr iova attribute

Remove mr iova attribute because we don't want to pass up kernel pointers.

Fixes: fccec5b8 ("RDMA/nldev: provide detailed MR information")
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>