iwlwifi: fix remove key error

Fix following error by sending synchronous command and waiting for the command
to complete.

mac80211-phy0: failed to remove key (0, ff:ff:ff:ff:ff:ff) from hardware (-16).

-16 is EBUSY error. The asynchronous command tests for STATUS_EXIT_PENDING
while interface is getting down and it returns -EBUSY error if set.
Changing the host command from asynchronous call to synchronous call
enables command to be run while interface is going down.

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-sta.c b/drivers/net/wireless/iwlwifi/iwl-sta.c
index c6633fe..a2b9ec8 100644
--- a/drivers/net/wireless/iwlwifi/iwl-sta.c
+++ b/drivers/net/wireless/iwlwifi/iwl-sta.c
@@ -520,7 +520,7 @@
 	struct iwl_host_cmd cmd = {
 		.id = REPLY_WEPKEY,
 		.data = wep_cmd,
-		.flags = CMD_ASYNC,
+		.flags = CMD_SYNC,
 	};
 
 	memset(wep_cmd, 0, cmd_size +