[SCSI] libfc: Don't assume response request present.

Fix NULL pointer dereference crash occurs in fc_lport_bsg_request()
for bsg requests that do not contain a response request.
Specifically, FC_BSG_HST_ADD_RPORT and FC_BSG_HST_DEL_RPORT bsg
requests are not guaranteed to include a response request.

Signed-off-by: Hugh Daschbach <hdasch@broadcom.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/scsi/libfc/fc_lport.c

@@ -1800,7 +1800,8 @@ int fc_lport_bsg_request(struct fc_bsg_job *job)
 	u32 did;
 
 	job->reply->reply_payload_rcv_len = 0;
-	rsp->resid_len = job->reply_payload.payload_len;
+	if (rsp)
+		rsp->resid_len = job->reply_payload.payload_len;
 
 	mutex_lock(&lport->lp_mutex);