iwlwifi: mvm: fix a comment about the SP length

The SP length in the ADD_STA command is an actual number of
frames, and not the SP len as it appears in the WME IE.
Fix that comment. The actual code is fine.
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/fw/api/sta.h

@@ -8,6 +8,7 @@
  * Copyright(c) 2012 - 2014 Intel Corporation. All rights reserved.
  * Copyright(c) 2013 - 2014 Intel Mobile Communications GmbH
  * Copyright(c) 2016 - 2017 Intel Deutschland GmbH
+ * Copyright(c) 2018 Intel Corporation
  *
  * 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
@@ -30,6 +31,7 @@
  * Copyright(c) 2012 - 2014 Intel Corporation. All rights reserved.
  * Copyright(c) 2013 - 2014 Intel Mobile Communications GmbH
  * Copyright(c) 2016 - 2017 Intel Deutschland GmbH
+ * Copyright(c) 2018 Intel Corporation
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -391,7 +393,7 @@ enum iwl_sta_type {
  * @tfd_queue_msk: tfd queues used by this station.
  *	Obselete for new TX API (9 and above).
  * @rx_ba_window: aggregation window size
- * @sp_length: the size of the SP as it appears in the WME IE
+ * @sp_length: the size of the SP in actual number of frames
  * @uapsd_acs:  4 LS bits are trigger enabled ACs, 4 MS bits are the deliver
  *	enabled ACs.
  *