Btrfs: try to cleanup delayed refs while freeing extents

When extents are freed, it is likely that we've removed the last
delayed reference update for the extent.  This checks the delayed
ref tree when things are freed, and if no ref updates area left it
immediately processes the delayed ref.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
index 37919e5..c345fee 100644
--- a/fs/btrfs/delayed-ref.h
+++ b/fs/btrfs/delayed-ref.h
@@ -137,9 +137,8 @@
 			  u64 ref_generation, u64 owner_objectid, int action,
 			  int pin);
 
-struct btrfs_delayed_ref *
-btrfs_find_delayed_ref(struct btrfs_trans_handle *trans, u64 bytenr,
-		       u64 parent);
+struct btrfs_delayed_ref_head *
+btrfs_find_delayed_ref_head(struct btrfs_trans_handle *trans, u64 bytenr);
 int btrfs_delayed_ref_pending(struct btrfs_trans_handle *trans, u64 bytenr);
 int btrfs_lock_delayed_ref(struct btrfs_trans_handle *trans,
 			   struct btrfs_delayed_ref_node *ref,