firewire: sbp2: Ignore SBP-2 targets on the local node

The firewire-sbp2 module tries to login to an SBP-2/3 target even when
it is running on the local node, which fails because of the inability to
fetch data from DMA mapped regions using firewire transactions on the
local node. It also doesn't make much sense to have the initiator and
target on the same node, so this patch prevents this behaviour.

Signed-off-by: Chris Boot <bootc@bootc.net>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> (changed the comment)