bdi: Rename cgwb_bdi_destroy() to cgwb_bdi_unregister()

Rename cgwb_bdi_destroy() to cgwb_bdi_unregister() as it gets called
from bdi_unregister() which is not necessarily called from bdi_destroy()
and thus the name is somewhat misleading.
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

mm/backing-dev.c

@@ -700,7 +700,7 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi)
 	return ret;
 }
 
-static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
+static void cgwb_bdi_unregister(struct backing_dev_info *bdi)
 {
 	struct radix_tree_iter iter;
 	void **slot;
@@ -801,7 +801,7 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi)
 	return 0;
 }
 
-static void cgwb_bdi_destroy(struct backing_dev_info *bdi) { }
+static void cgwb_bdi_unregister(struct backing_dev_info *bdi) { }
 
 static void cgwb_bdi_exit(struct backing_dev_info *bdi)
 {
@@ -925,7 +925,7 @@ void bdi_unregister(struct backing_dev_info *bdi)
 	/* make sure nobody finds us on the bdi_list anymore */
 	bdi_remove_from_list(bdi);
 	wb_shutdown(&bdi->wb);
-	cgwb_bdi_destroy(bdi);
+	cgwb_bdi_unregister(bdi);
 
 	if (bdi->dev) {
 		bdi_debug_unregister(bdi);