s390/pci: remove unused bus_next field from struct zpci_dev

This field was added in commit 44510d6f ("s390/pci: Handling
multifunctions") but is an unused remnant of an earlier version where
the devices on the virtual bus were connected in a linked list instead
of a fixed 256 entry array of pointers.

It is also not used for the list of busses as that is threaded through
struct zpci_bus not through struct zpci_dev.
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/pci.h

@@ -117,7 +117,6 @@ struct zpci_bus {
 struct zpci_dev {
 	struct zpci_bus *zbus;
 	struct list_head entry;		/* list of all zpci_devices, needed for hotplug, etc. */
-	struct list_head bus_next;
 	struct kref kref;
 	struct hotplug_slot hotplug_slot;