ieee1394: write broadcast_channel only to select nodes (fixes device recognition)

ieee1394: write broadcast_channel only to select nodes (fixes device recognition)

Some old 1394-1995 SBP-2 bridges would hang if they received a broadcast write
request to BROADCAST_CHANNEL before the config ROM was read.  Affected devices
include Datafab MD2-FW2 2.5" HDD and SmartDisk VST FWCDRW-V8 portable CD writer.
The write request is now directed to specific nodes instead of being broadcast
to all nodes at once, and it is only performed if a previous read request at
this register succeeded.

Fixes an old interoperability problem which was perceived as a 2.6.14-specific
regression: http://marc.theaimsgroup.com/?t=113190586800003

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Jody McIntyre <scjody@modernduck.com>