ptp: fix code indentation issues

This fixes the following checkpatch.pl errors:

ERROR: code indent should use tabs where possible
+^I        if (ptp->pps_source)$

ERROR: code indent should use tabs where possible
+^I                pps_unregister_source(ptp->pps_source);$

ERROR: code indent should use tabs where possible
+^I                kthread_destroy_worker(ptp->kworker);$

Fixes: 4225fea1 ("ptp: Fix possible memory leak in ptp_clock_register()")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>