drm/cma: Remove call to drm_gem_free_mmap_offset()

drm_gem_object_release() called later in the drm_gem_cma_free_object()
function already calls this, so there's no need to do this explicitly.
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/drm_gem_cma_helper.c

@@ -187,8 +187,6 @@ void drm_gem_cma_free_object(struct drm_gem_object *gem_obj)
 {
 	struct drm_gem_cma_object *cma_obj;
 
-	drm_gem_free_mmap_offset(gem_obj);
-
 	cma_obj = to_drm_gem_cma_obj(gem_obj);
 
 	if (cma_obj->vaddr) {