bcache: Convert debug code to btree_keys

More work to disentangle various code from struct btree

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 6d6a7a1..24a3a15 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -384,7 +384,7 @@
 			break;
 	}
 
-	bch_bkey_to_text(buf, sizeof(buf), k);
+	bch_extent_to_text(buf, sizeof(buf), k);
 	pr_debug("%s UUIDs at %s", rw & REQ_WRITE ? "wrote" : "read", buf);
 
 	for (u = c->uuids; u < c->uuids + c->nr_uuids; u++)