s390/pci: remove superfluous zdev->zbus check

Checking zdev->zbus for NULL in __zpci_event_availability() is
superfluous as it can never be NULL at this point. While harmless this
check causes smatch warnings because we later access zdev->zbus with
only having checked zdev != NULL which is sufficient.

The reason zdev->zbus can never be NULL is since with zdev != NULL given
we know the zdev came from get_zdev_by_fid() and thus the zpci_list.
Now on first glance at zpci_create_device() one may assume that there is
a window where the zdev is in the list without a zdev, however this
window can't overlap with __zpci_event_availability() as
zpci_create_device() either runs on the same kthread as part of
availability events, or during the initial CLP List PCI at which point
the __zpci_event_availability() is not yet called as zPCI is not yet
initialized.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/pci/pci_event.c

@@ -80,7 +80,7 @@ static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf)
 	enum zpci_state state;
 	int ret;
 
-	if (zdev && zdev->zbus && zdev->zbus->bus)
+	if (zdev && zdev->zbus->bus)
 		pdev = pci_get_slot(zdev->zbus->bus, zdev->devfn);
 
 	zpci_err("avail CCDF:\n");