rtlwifi: rtl8192cu: Fix W=1 build warning

When this driver is built with "make W=1", the following warning is output:

drivers/net/wireless/rtlwifi/rtl8192cu/sw.c:56:6: warning: variable ‘err’ set but not used [-Wunused-but-set-variable]
Signed-off-by: NLarry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rtlwifi/rtl8192cu/sw.c

@@ -76,7 +76,7 @@ static int rtl92cu_init_sw_vars(struct ieee80211_hw *hw)
 				      GFP_KERNEL, hw, rtl_fw_cb);
 
 
-	return 0;
+	return err;
 }
 
 static void rtl92cu_deinit_sw_vars(struct ieee80211_hw *hw)