lanai: use pci_dev->subsystem_device

The driver reads PCI subsystem IDs from the PCI configuration registers while
it is already stored by the PCI subsystem in the 'subsystem_device' field of
'struct pci_dev'...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>