Btrfs: add missing kfree in btrfs_destroy_workqueue

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
index 00623dd..66532b8 100644
--- a/fs/btrfs/async-thread.c
+++ b/fs/btrfs/async-thread.c
@@ -315,6 +315,7 @@
 	if (wq->high)
 		__btrfs_destroy_workqueue(wq->high);
 	__btrfs_destroy_workqueue(wq->normal);
+	kfree(wq);
 }
 
 void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int max)