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: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Jarod Wilson <jwilson@redhat.com>