IB/srp: Fail I/O fast if target offline

If reconnecting failed we know that no command completion will
be received anymore.  Hence let the SCSI error handler fail such
commands immediately.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: David Dillow <dillowda@ornl.gov>
Signed-off-by: Roland Dreier <roland@purestorage.com>