asahi: fix zero bo leak

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34486>

src/asahi/lib/agx_device.c

@@ -670,6 +670,8 @@ agx_open_device(void *memctx, struct agx_device *dev)
          fprintf(stderr, "Failed to bind zero page");
          return false;
       }
+
+      dev->zero_bo = bo;
    }
 
    void *bo = agx_bo_create(dev, LIBAGX_PRINTF_BUFFER_SIZE, 0, AGX_BO_WRITEBACK,
@@ -691,6 +693,7 @@ void
 agx_close_device(struct agx_device *dev)
 {
    agx_bo_unreference(dev, dev->printf.bo);
+   agx_bo_unreference(dev, dev->zero_bo);
    u_printf_destroy(&dev->printf);
    agx_bo_cache_evict_all(dev);
    util_sparse_array_finish(&dev->bo_map);

src/asahi/lib/agx_device.h

@@ -133,6 +133,8 @@ struct agx_device {
     */
    uint64_t sparse_ro_offset;
 
+   struct agx_bo *zero_bo;
+
    struct renderonly *ro;
 
    pthread_mutex_t bo_map_lock;