You can't update two tables or two different rows in one statement - you need to do two UPDATE statements, preferably as part of a TRANSACTION.
Personnaly, I would create a Stored Procedure to do them both within a transaction:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE PROCEDURE MoveGoods
AS
BEGIN
SET NOCOUNT ON;
BEGIN TRANSACTION
UPDATE prod_inventory SET qty = qty-5 WHERE prodId = 1 AND WarehouseId=1
UPDATE prod_inventory SET qty = qty+5 WHERE prodId = 1 AND WarehouseId=2
COMMIT
END
GO