pwc: Add support for control events

Since the pwc driver already uses v4l2-device, v4l2-fh, and the control
framework, all that is needed is hooking up event subscription.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/pwc/pwc-v4l.c

@@ -1166,4 +1166,6 @@ const struct v4l2_ioctl_ops pwc_ioctl_ops = {
 	.vidioc_enum_frameintervals	    = pwc_enum_frameintervals,
 	.vidioc_g_parm			    = pwc_g_parm,
 	.vidioc_s_parm			    = pwc_s_parm,
+	.vidioc_subscribe_event		    = v4l2_ctrl_subscribe_event,
+	.vidioc_unsubscribe_event	    = v4l2_event_unsubscribe,
 };