firewire: Complete SCSI commands with DID_BUS_BUSY when a bus reset happens.

This lets the SCSI stack retry the command when a SCSI command is
interrupted by a FireWire bus reset.

Signed-off-by: Kristian Høgsberg <krh@redhat.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>