PTP: convert class code to use dev_groups

The dev_attrs field of struct class is going away soon, dev_groups
should be used instead.  This converts the ptp class code to use the
correct field.

Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index 4a8c388..a8319b2 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -330,7 +330,7 @@
 		goto no_region;
 	}
 
-	ptp_class->dev_attrs = ptp_dev_attrs;
+	ptp_class->dev_groups = ptp_groups;
 	pr_info("PTP clock support registered\n");
 	return 0;