ieee1394: nodemgr: fix deadlock in shutdown

ieee1394: nodemgr: fix deadlock in shutdown

If "modprobe ohci1394" was quickly followed by "modprobe -r ohci1394",
say with 1 second pause in between, the modprobe -r got stuck in
uninterruptible sleep in kthread_stop.  At the same time the knodemgrd
slept uninterruptibly in bus_rescan_devices_helper.  That's because
driver_detach took the semaphore of the PCI device and
bus_rescan_devices_helper wanted to take the semaphore of the FireWire
host device's parent, which is the same semaphore. This was a regression
since Linux 2.6.16, commit bf74ad5bc41727d5f2f1c6bedb2c1fac394de731,
"Hold the device's parent's lock during probe and remove".

The fix (or workaround) adds a dummy driver to the hpsb_host device. Now
bus_rescan_devices_helper won't scan the host device anymore.  This
doesn't hurt since we have no drivers which will bind to these devices
and it is unlikely that there will ever be such a driver.  The dummy
driver is befittingly presented as a representation of ieee1394 itself.

Fixes: http://bugzilla.kernel.org/show_bug.cgi?id=6706

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>