net: ethernet: ti: cpts: fix registration order

The ptp clock registered before spinlock, which is protecting it, and
before timecounter and cyclecounter initialization in cpts_register().

So, ensure that ptp clock is registered the last, after everything
else is done.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>