PCI/XEN: Fix bug introduced by a recent change

This patch (as1516) fixes a bug introduced during the removal of
put_driver() and get_driver() from drivers/pci/xen-pcifront.c.
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/pci/xen-pcifront.c

@@ -593,7 +593,7 @@ static pci_ers_result_t pcifront_common_process(int cmd,
 	}
 	pdrv = pcidev->driver;
 
-	if (pdrv->driver) {
+	if (pdrv) {
 		if (pdrv->err_handler && pdrv->err_handler->error_detected) {
 			dev_dbg(&pcidev->dev,
 				"trying to call AER service\n");