net/virtio: do not store PCI device pointer at shared memory

hw->dev, a pointer to pci_dev, was actually not used, until the
refactor of decouping from PCI device. This would somehow break
the multiple process again, since "hw" is stored at shared memory,
while "pci_dev" is not: the primary and secondary process could
have different address for it, while just one value is allowed.

Thus we should not store it to "hw", instead, we could retrieve
it from the "eth_dev->device" field.

Fixes: ae34410a8a8a ("ethdev: move info filling of PCI into drivers")
Fixes: eac901ce29be ("ethdev: decouple from PCI device")

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>