ieee1394: inherit ud vendor_id from node vendor_id

While Module_Vendor_ID in the configuration ROM's root directory is
mandatory, there often aren't vendor IDs in unit directories.  This
affects the new firedtv driver which is meant to be auto-loaded and
matched only for vendor-specific devices.

We now always copy ne->vendor_id into ud->vendor_id before we scan a
unit directory (and fill in a possibly present vendor ID from there).
This way, the root directory's vendor ID is used as fallback in the
"uevent" environment for modprobe'ing per module alias when a node was
plugged in, and in the driver match routine when protocol drivers are
bound to unit directories.  It will however not be used as sysfs
attribute of a unit directory device.

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