asahi: plug glsl type leak

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27616>

src/asahi/lib/agx_device.c

@@ -359,6 +359,7 @@ agx_close_device(struct agx_device *dev)
 
    util_vma_heap_finish(&dev->main_heap);
    util_vma_heap_finish(&dev->usc_heap);
+   glsl_type_singleton_decref();
 
    close(dev->fd);
 }