wlr_virtual_pointer_v1: fix discrete scrolling

It seems it was forgotten to adjust when implementing
	!3461 High-resolution scroll wheel support

types/wlr_virtual_pointer_v1.c

@@ -180,7 +180,8 @@ static void virtual_pointer_axis_discrete(struct wl_client *client,
 	pointer->axis_event[pointer->axis].time_msec = time;
 	pointer->axis_event[pointer->axis].orientation = axis;
 	pointer->axis_event[pointer->axis].delta = wl_fixed_to_double(value);
-	pointer->axis_event[pointer->axis].delta_discrete = discrete;
+	pointer->axis_event[pointer->axis].delta_discrete = discrete *
+		WLR_POINTER_AXIS_DISCRETE_STEP;
 }
 
 static void virtual_pointer_destroy_resource(struct wl_resource *resource) {