RDS: IB: Remove an unused structure member

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: linux-rdma@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: rds-devel@oss.oracle.com
Signed-off-by: Doug Ledford <dledford@redhat.com>