drm: Use the driver's gem_object_free function from CMA helpers.

VC4 wraps the CMA objects in its own structures, so it needs to do its
own teardown (waiting for GPU to finish, updating bo_stats tracking).
The other CMA drivers are using drm_gem_cma_free_object as their
gem_free_object, so this should be a no-op for them.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
index 0f7b00b..e5df53b 100644
--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -121,7 +121,7 @@
 	return cma_obj;
 
 error:
-	drm_gem_cma_free_object(&cma_obj->base);
+	drm->driver->gem_free_object(&cma_obj->base);
 	return ERR_PTR(ret);
 }
 EXPORT_SYMBOL_GPL(drm_gem_cma_create);
@@ -171,7 +171,7 @@
 	return cma_obj;
 
 err_handle_create:
-	drm_gem_cma_free_object(gem_obj);
+	drm->driver->gem_free_object(gem_obj);
 
 	return ERR_PTR(ret);
 }