pcnet32: VLB support fixes

VLB support has been broken since at least 2004-2005 period as some
changes introduced back then assumed that ->pci_dev is always valid,
lets try to fix it:

- remove duplicated SET_NETDEV_DEV() call

- call SET_NETDEV_DEV() only for PCI devices

- check for ->pci_dev validity in pcnet32_open()

[ Alternatively we may consider removing VLB support but there would not
  be much gain in it since an extra driver code needed for VLB support is
  minimal and quite simple. ]

This takes care of the following entry from Dan's list:

drivers/net/pcnet32.c +1889 pcnet32_probe1(298) warning: variable derefenced before check 'pdev'

Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Acked-by: Don Fry <pcnet32@verizon.net>
Signed-off-by: David S. Miller <davem@davemloft.net>