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/extents.h b/drivers/md/bcache/extents.h
index e0c0b68..e4e2340 100644
--- a/drivers/md/bcache/extents.h
+++ b/drivers/md/bcache/extents.h
@@ -7,6 +7,7 @@
 struct bkey;
 struct cache_set;
 
+void bch_extent_to_text(char *, size_t, const struct bkey *);
 bool __bch_btree_ptr_invalid(struct cache_set *, const struct bkey *);
 
 #endif /* _BCACHE_EXTENTS_H */