firewire-core uses fw_card.lock to protect topology data and transaction
data. firewire-sbp2 uses fw_card.lock for entirely unrelated purposes.
Introduce a sbp2_target.lock to firewire-sbp2 and replace all
fw_card.lock uses in the driver. fw_card.lock is now entirely private
to firewire-core. This has no immediate advantage apart from making it
clear in the code that firewire-sbp2 does not interact with the core
via the core lock.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
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