ieee1394: sbp2: recheck node generation in sbp2_update

While sbp2_update() is doing its duties after a bus reset, another reset
could happen.  Don't accept new requests until the next undisturbed
sbp2_update() or until sbp2_remove().

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

diff --cc drivers/ieee1394/sbp2.c
Simple merge