ipw2x00: remove set but not used variable 'reason'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/wireless/intel/ipw2x00/ipw2200.c: In function ipw_wx_set_mlme:
drivers/net/wireless/intel/ipw2x00/ipw2200.c:6805:9: warning: variable reason set but not used [-Wunused-but-set-variable]
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/intel/ipw2x00/ipw2200.c

@@ -6788,9 +6788,6 @@ static int ipw_wx_set_mlme(struct net_device *dev,
 {
 	struct ipw_priv *priv = libipw_priv(dev);
 	struct iw_mlme *mlme = (struct iw_mlme *)extra;
-	__le16 reason;
-
-	reason = cpu_to_le16(mlme->reason_code);
 
 	switch (mlme->cmd) {
 	case IW_MLME_DEAUTH: