idpf: fix aux device unplugging when rdma is not supported by vport

In the Linux kernel, the following vulnerability has been resolved: idpf: fix aux device unplugging when rdma is not supported by vport If vport flags do not contain VIRTCHNL2_VPORT_ENABLE_RDMA, driver does not allocate vdev_info for this vport. This leads to kernel NULL pointer dereference in idpf_idc_vport_dev_down(), which references vdev_info for every vport regardless. Check, if vdev_info was ever allocated before unplugging aux device.