[SCSI] zfcp: Fix tracing of requests with error status

When a FSF request is returned with an error it should be reported
through blktrace for the ziomon tools, but the latency information
should not be read. Fix this by also calling zfcp_fsf_req_trace for
the error case, but skip reading the latencies inside the function.

Reviewed-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>