staging: rtl8723bs: core: rtw_mlme: 'retry' is only used if REJOIN is set

Fixes the following W=1 kernel build warning(s):

 drivers/staging/rtl8723bs/core/rtw_mlme.c: In function ‘rtw_joinbss_event_prehandle’:
 drivers/staging/rtl8723bs/core/rtw_mlme.c:1192:12: warning: variable ‘retry’ set but not used [-Wunused-but-set-variable]

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Fabio Aiuto <fabioaiuto83@gmail.com>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210414181129.1628598-32-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/core/rtw_mlme.c

@@ -1189,7 +1189,7 @@ static void rtw_joinbss_update_network(struct adapter *padapter, struct wlan_net
 /* define REJOIN */
 void rtw_joinbss_event_prehandle(struct adapter *adapter, u8 *pbuf)
 {
-	static u8 retry;
+	static u8 __maybe_unused retry;
 	struct sta_info *ptarget_sta = NULL, *pcur_sta = NULL;
 	struct	sta_priv *pstapriv = &adapter->stapriv;
 	struct	mlme_priv *pmlmepriv = &(adapter->mlmepriv);