rtl8xxxu: Remove set but not used variable 'rsr'

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

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c: In function rtl8xxxu_gen2_config_channel:
drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c:1266:13: warning: variable rsr set but not used [-Wunused-but-set-variable]

rsr is never used, so remove it.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Reviewed-by: Chris Chiu <chiu@endlessm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c

@@ -1255,7 +1255,7 @@ void rtl8xxxu_gen1_config_channel(struct ieee80211_hw *hw)
 void rtl8xxxu_gen2_config_channel(struct ieee80211_hw *hw)
 {
 	struct rtl8xxxu_priv *priv = hw->priv;
-	u32 val32, rsr;
+	u32 val32;
 	u8 val8, subchannel;
 	u16 rf_mode_bw;
 	bool ht = true;
@@ -1264,7 +1264,6 @@ void rtl8xxxu_gen2_config_channel(struct ieee80211_hw *hw)
 
 	rf_mode_bw = rtl8xxxu_read16(priv, REG_WMAC_TRXPTCL_CTL);
 	rf_mode_bw &= ~WMAC_TRXPTCL_CTL_BW_MASK;
-	rsr = rtl8xxxu_read32(priv, REG_RESPONSE_RATE_SET);
 	channel = hw->conf.chandef.chan->hw_value;
 
 /* Hack */