PCI: Be a bit defensive in quirk_nvidia_ck804() so we don't risk dereferencing a NULL pdev.

pci_get_slot() may return NULL if nothing was found.  quirk_nvidia_ck804()
does not check the value returned from pci_get_slot(), so it may end up
causing a NULL pointer deref.
Signed-off-by: NJesper Juhl <jesper.juhl@gmail.com>
Acked-by: NAlan Cox <alan@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/pci/quirks.c

@@ -1743,6 +1743,8 @@ static void __devinit quirk_nvidia_ck804_msi_ht_cap(struct pci_dev *dev)
 	 * a single one having MSI is enough to be sure that MSI are supported.
 	 */
 	pdev = pci_get_slot(dev->bus, 0);
+	if (!pdev)
+		return;
 	if (!msi_ht_cap_enabled(dev) && !msi_ht_cap_enabled(pdev)) {
 		printk(KERN_WARNING "PCI: MSI quirk detected. "
 		       "MSI disabled on chipset %s.\n",