iwlwifi: trans: fix iwl_trans_txq_scd_cfg.sta_id sign

For some reason, this was defined as a signed variable.
Make it unsigned.
Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

drivers/net/wireless/intel/iwlwifi/iwl-trans.h

@@ -7,6 +7,7 @@
  *
  * Copyright(c) 2007 - 2014 Intel Corporation. All rights reserved.
  * Copyright(c) 2013 - 2015 Intel Mobile Communications GmbH
+ * Copyright(c) 2016        Intel Deutschland GmbH
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of version 2 of the GNU General Public License as
@@ -33,6 +34,7 @@
  *
  * Copyright(c) 2005 - 2014 Intel Corporation. All rights reserved.
  * Copyright(c) 2013 - 2015 Intel Mobile Communications GmbH
+ * Copyright(c) 2016        Intel Deutschland GmbH
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -519,7 +521,7 @@ struct iwl_trans;
 
 struct iwl_trans_txq_scd_cfg {
 	u8 fifo;
-	s8 sta_id;
+	u8 sta_id;
 	u8 tid;
 	bool aggregate;
 	int frame_limit;