firewire: ohci: fix DMA unmapping in an error path

If request_irq failed, we would pass wrong arguments to
dma_free_coherent.  https://bugzilla.redhat.com/show_bug.cgi?id=728185

Reported-by: Mads Kiilerich
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/ohci.c

@@ -2178,8 +2178,13 @@ static int ohci_enable(struct fw_card *card,
 			ohci_driver_name, ohci)) {
 		fw_error("Failed to allocate interrupt %d.\n", dev->irq);
 		pci_disable_msi(dev);
-		dma_free_coherent(ohci->card.device, CONFIG_ROM_SIZE,
-				  ohci->config_rom, ohci->config_rom_bus);
+
+		if (config_rom) {
+			dma_free_coherent(ohci->card.device, CONFIG_ROM_SIZE,
+					  ohci->next_config_rom,
+					  ohci->next_config_rom_bus);
+			ohci->next_config_rom = NULL;
+		}
 		return -EIO;
 	}