drm/fb-dma-helper: Test for imported buffers with drm_gem_is_imported()

Instead of testing import_attach for imported GEM buffers, invoke
drm_gem_is_imported() to do the test.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Anusha Srivatsa <asrivats@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250226172457.217725-9-tzimmermann@suse.de

Author: Thomas Zimmermann

drivers/gpu/drm/drm_fb_dma_helper.c

@@ -178,7 +178,7 @@ int drm_fb_dma_get_scanout_buffer(struct drm_plane *plane,
 	dma_obj = drm_fb_dma_get_gem_obj(fb, 0);
 
 	/* Buffer should be accessible from the CPU */
-	if (dma_obj->base.import_attach)
+	if (drm_gem_is_imported(&dma_obj->base))
 		return -ENODEV;
 
 	/* Buffer should be already mapped to CPU */