ptp: unregister virtual clocks when unregistering physical clock.

When unregistering a physical clock which has some virtual clocks,
unregister the virtual clocks with it.

This fixes the following oops, which can be triggered by unloading
a driver providing a PTP clock when it has enabled virtual clocks:

BUG: unable to handle page fault for address: ffffffffc04fc4d8
Oops: 0000 [#1] PREEMPT SMP NOPTI
RIP: 0010:ptp_vclock_read+0x31/0xb0
Call Trace:
 timecounter_read+0xf/0x50
 ptp_vclock_refresh+0x2c/0x50
 ? ptp_clock_release+0x40/0x40
 ptp_aux_kworker+0x17/0x30
 kthread_worker_fn+0x9b/0x240
 ? kthread_should_park+0x30/0x30
 kthread+0xe2/0x110
 ? kthread_complete_and_exit+0x20/0x20
 ret_from_fork+0x22/0x30

Fixes: 73f3706 ("ptp: support ptp physical/virtual clocks conversion")
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Cc: Yangbo Lu <yangbo.lu@nxp.com>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/ptp/ptp_clock.c

@@ -317,11 +317,18 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
 }
 EXPORT_SYMBOL(ptp_clock_register);
 
+static int unregister_vclock(struct device *dev, void *data)
+{
+	struct ptp_clock *ptp = dev_get_drvdata(dev);
+
+	ptp_vclock_unregister(info_to_vclock(ptp->info));
+	return 0;
+}
+
 int ptp_clock_unregister(struct ptp_clock *ptp)
 {
 	if (ptp_vclock_in_use(ptp)) {
-		pr_err("ptp: virtual clock in use\n");
-		return -EBUSY;
+		device_for_each_child(&ptp->dev, NULL, unregister_vclock);
 	}
 
 	ptp->defunct = 1;