cmd640: fix kernel oops in test_irq() method

When implementing the test_iqr() method, I forgot that this driver is not an
ordinary PCI driver and also needs to support VLB variant of the chip. Moreover,
'hwif->dev' should be NULL, potentially causing oops in pci_read_config_byte().

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