bcache: remove "XXX:" comment line from run_cache_set()

In previous bcache patches for Linux v5.2, the failure code path of
run_cache_set() is tested and fixed. So now the following comment
line can be removed from run_cache_set(),
	/* XXX: test this, it's broken */

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/super.c

@@ -1979,7 +1979,7 @@ err:
 	}
 
 	closure_sync(&cl);
-	/* XXX: test this, it's broken */
+
 	bch_cache_set_error(c, "%s", err);
 
 	return -EIO;