firewire: fw-ohci: catch self_id_count == 0

fw_core_handle_bus_reset() incorrectly relied on the assumption that
self_id_count > 0.

We check early in fw-ohci and discard the self ID complete event if
self_id_count == 0 because a valid event always has at least one self ID
packet in it (the one of the local node).  Hence treat self_id_count ==
0 like any other kind of invalid self ID buffer.
Signed-off-by: NStefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: NJarod Wilson <jwilson@redhat.com>

drivers/firewire/fw-ohci.c

@@ -1031,6 +1031,10 @@ static void bus_reset_tasklet(unsigned long data)
 	 * bit extra to get the actual number of self IDs.
 	 */
 	self_id_count = (reg >> 3) & 0x3ff;
+	if (self_id_count == 0) {
+		fw_notify("inconsistent self IDs\n");
+		return;
+	}
 	generation = (cond_le32_to_cpu(ohci->self_id_cpu[0]) >> 16) & 0xff;
 	rmb();