dm writecache: fix typo in name for writeback_wq

The workqueue's name should be "writecache-writeback" instead of
"writecache-writeabck".
Signed-off-by: Huaisheng Ye <yehs1@lenovo.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-writecache.c

@@ -1859,7 +1859,7 @@ static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv)
 		goto bad;
 	}
 
-	wc->writeback_wq = alloc_workqueue("writecache-writeabck", WQ_MEM_RECLAIM, 1);
+	wc->writeback_wq = alloc_workqueue("writecache-writeback", WQ_MEM_RECLAIM, 1);
 	if (!wc->writeback_wq) {
 		r = -ENOMEM;
 		ti->error = "Could not allocate writeback workqueue";