Fixed the serial mouse wheel.

src/device/mouse.c

@@ -347,6 +347,14 @@ mouse_subtract_coords(int *delta_x, int *delta_y, int *o_x, int *o_y,
     mouse_subtract_y(delta_y, o_y, min, max, invert, abs);
 }
 
+int
+mouse_wheel_moved(void)
+{
+    int ret = !!(atomic_load(&mouse_z));
+
+    return ret;
+}
+
 int
 mouse_moved(void)
 {