ptp: reorder declarations in ptp_ioctl()

Reorder declarations of variables as reversed Christmas tree.

Cc: Richard Cochran <richardcochran@gmail.com>
Suggested-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>