virtio: Remove unnecessary variable assignments

In function vp_modern_probe(), "pci_dev" is initialized with the
value of "mdev->pci_dev", so assigning "pci_dev" to "mdev->pci_dev"
is unnecessary since they store the same value.

Signed-off-by: Bo Liu <liubo03@inspur.com>
Message-Id: <20220617055952.5364-1-liubo03@inspur.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>