Btrfs: Fix memory leak on finding existing super

We missed a memory deallocation in commit 450ba0ea.

If an existing super block is found at mount and there is no
error condition then the pre-allocated tree_root and fs_info
are no not used and are not freeded.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 61bd79a..f50253c 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -654,6 +654,8 @@
 		}
 
 		btrfs_close_devices(fs_devices);
+		kfree(fs_info);
+		kfree(tree_root);
 	} else {
 		char b[BDEVNAME_SIZE];