[netdrvr pcnet32] fix oops on unload

Driver was calling pci_unregister_driver for each _device_, and then
again at the end of the module unload routine.  Remove the call that's
inside the loop, pci_unregister_driver should only be called once.

Caught by Don Fry (and many others)

drivers/net/pcnet32.c

@@ -1766,8 +1766,6 @@ static void __exit pcnet32_cleanup_module(void)
 	next_dev = lp->next;
 	unregister_netdev(pcnet32_dev);
 	release_region(pcnet32_dev->base_addr, PCNET32_TOTAL_SIZE);
-	if (lp->pci_dev)
-	    pci_unregister_driver(&pcnet32_driver);
 	pci_free_consistent(lp->pci_dev, sizeof(*lp), lp, lp->dma_addr);
 	free_netdev(pcnet32_dev);
 	pcnet32_dev = next_dev;