ptp: Set lookup cookie when creating a PTP PPS source.

When creating a PTP device, the configuration block allows
creation of an associated PPS device.  However, there isn't
any way to associate the two devices after creation.

Set the PPS cookie, so pps_lookup_dev(ptp) performs correctly.
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/ptp/ptp_clock.c

@@ -218,6 +218,7 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
 			pr_err("failed to create ptp aux_worker %d\n", err);
 			goto kworker_err;
 		}
+		ptp->pps_source->lookup_cookie = ptp;
 	}
 
 	err = ptp_populate_pin_groups(ptp);