iwlwifi: mvm: make num_active_macs unsigned

There is no point in having num_active_macs signed
since it should never be negative. Set it to be an
unsigned variable to ensure this.
Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/sf.c

@@ -7,6 +7,7 @@
  *
  * Copyright(c) 2013 - 2014 Intel Corporation. All rights reserved.
  * Copyright(c) 2013 - 2014 Intel Mobile Communications 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
@@ -28,6 +29,7 @@
  *
  * Copyright(c) 2013 - 2014 Intel Corporation. All rights reserved.
  * Copyright(c) 2013 - 2014 Intel Mobile Communications GmbH
+ * Copyright (C) 2018 Intel Corporation
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -64,7 +66,7 @@ struct iwl_mvm_active_iface_iterator_data {
 	struct ieee80211_vif *ignore_vif;
 	u8 sta_vif_ap_sta_id;
 	enum iwl_sf_state sta_vif_state;
-	int num_active_macs;
+	u32 num_active_macs;
 };
 
 /*