Btrfs: properly reset block cache on free

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 21f39b40..7f156d9 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -182,7 +182,7 @@
 		}
 		ret = btrfs_del_item(extent_root, &path);
 		if (root != extent_root &&
-		    extent_root->last_insert.objectid < blocknr)
+		    extent_root->last_insert.objectid > blocknr)
 			extent_root->last_insert.objectid = blocknr;
 		if (ret)
 			BUG();