ptp: Relocate lookup cookie to correct block.

An earlier commit set the pps_lookup cookie, but the line
was somehow added to the wrong code block.  Correct this.

Fixes: 8602e40f ("ptp: Set lookup cookie when creating a PTP PPS source.")
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: Dario Binacchi <dariobin@libero.it>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>