linux-v4l2: Update properties when devices change.

This causes the properties for v4l2 sources to be refreshed when a
device is disconnected/connected.

plugins/linux-v4l2/v4l2-input.c

@@ -581,6 +581,8 @@ static void device_added(const char *dev, void *vptr)
 {
 	V4L2_DATA(vptr);
 
+	obs_source_update_properties(data->source);
+
 	if (strcmp(data->device_id, dev))
 		return;
 
@@ -597,6 +599,8 @@ static void device_removed(const char *dev, void *vptr)
 {
 	V4L2_DATA(vptr);
 
+	obs_source_update_properties(data->source);
+
 	if (strcmp(data->device_id, dev))
 		return;