pcnet32: Use pci_resource_len to validate PCI resource

pci_resource_start() is not a good indicator to determine if a PCI
resource exists or not, since the resource may start at address 0.
This is seen when trying to instantiate the driver in qemu for riscv32
or riscv64.

pci 0000:00:01.0: reg 0x10: [io  0x0000-0x001f]
pci 0000:00:01.0: reg 0x14: [mem 0x00000000-0x0000001f]
...
pcnet32: card has no PCI IO resources, aborting

Use pci_resouce_len() instead.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/amd/pcnet32.c

@@ -1534,8 +1534,7 @@ pcnet32_probe_pci(struct pci_dev *pdev, const struct pci_device_id *ent)
 	}
 	pci_set_master(pdev);
 
-	ioaddr = pci_resource_start(pdev, 0);
-	if (!ioaddr) {
+	if (!pci_resource_len(pdev, 0)) {
 		if (pcnet32_debug & NETIF_MSG_PROBE)
 			pr_err("card has no PCI IO resources, aborting\n");
 		err = -ENODEV;
@@ -1548,6 +1547,8 @@ pcnet32_probe_pci(struct pci_dev *pdev, const struct pci_device_id *ent)
 			pr_err("architecture does not support 32bit PCI busmaster DMA\n");
 		goto err_disable_dev;
 	}
+
+	ioaddr = pci_resource_start(pdev, 0);
 	if (!request_region(ioaddr, PCNET32_TOTAL_SIZE, "pcnet32_probe_pci")) {
 		if (pcnet32_debug & NETIF_MSG_PROBE)
 			pr_err("io address range already allocated\n");