drm/vc4: fix an error code

"exec->exec_bo" is NULL at this point so this code returns success.  We
want to return -ENOMEM.

Fixes: d5b1a78a ('drm/vc4: Add support for drawing 3D frames.')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/vc4/vc4_gem.c

@@ -580,7 +580,7 @@ vc4_get_bcl(struct drm_device *dev, struct vc4_exec_info *exec)
 	bo = vc4_bo_create(dev, exec_size, true);
 	if (!bo) {
 		DRM_ERROR("Couldn't allocate BO for binning\n");
-		ret = PTR_ERR(exec->exec_bo);
+		ret = -ENOMEM;
 		goto fail;
 	}
 	exec->exec_bo = &bo->base;