btrfs: fix unbalanced unlock in qgroup_account_snapshot()

qgroup_account_snapshot() is trying to unlock the not taken
tree_log_mutex in a error path. Since ret != 0 in this case, we can
just return from here.

Fixes: 2a4d84c1 ("btrfs: move delayed ref flushing for qgroup into qgroup helper")
CC: stable@vger.kernel.org # 5.12+
Reviewed-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NNaohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/transaction.c

@@ -1478,7 +1478,7 @@ static int qgroup_account_snapshot(struct btrfs_trans_handle *trans,
 	ret = btrfs_run_delayed_refs(trans, (unsigned long)-1);
 	if (ret) {
 		btrfs_abort_transaction(trans, ret);
-		goto out;
+		return ret;
 	}
 
 	/*