drm/tegra: Use dma_buf from GEM object instance

Avoid dereferencing struct drm_gem_object.import_attach for the
imported dma-buf. The dma_buf field in the GEM object instance refers
to the same buffer. Prepares to make import_attach an implementation
detail of PRIME.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20250619113100.70292-3-tzimmermann@suse.de

Author: tdz

drivers/gpu/drm/tegra/gem.c

@@ -526,7 +526,7 @@ void tegra_bo_free_object(struct drm_gem_object *gem)
 		if (drm_gem_is_imported(gem)) {
 			dma_buf_unmap_attachment_unlocked(gem->import_attach, bo->sgt,
 							  DMA_TO_DEVICE);
-			dma_buf_detach(gem->import_attach->dmabuf, gem->import_attach);
+			dma_buf_detach(gem->dma_buf, gem->import_attach);
 		}
 	}