staging: rtl8188eu: don't define OnAuth() in non-AP mode

If CONFIG_88EU_AP_MODE is undefined, OnAuth() is never referenced.

Fixes warning:
  drivers/staging/rtl8188eu/core/rtw_mlme_ext.c:2725:21: warning: ‘OnAuth’ defined but not used [-Wunused-function]
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Fixes: 68345dd7 ("staging: rtl8188eu: rtw_mlme_ext.c: unexport message callbacks")
Cc: Greg Kroah-Hartman <gregkh@linux.com>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/core/rtw_mlme_ext.c

@@ -2722,10 +2722,10 @@ static unsigned int OnBeacon(struct adapter *padapter,
 	return _SUCCESS;
 }
 
+#ifdef CONFIG_88EU_AP_MODE
 static unsigned int OnAuth(struct adapter *padapter,
 			   struct recv_frame *precv_frame)
 {
-#ifdef CONFIG_88EU_AP_MODE
 	unsigned int	auth_mode, ie_len;
 	u16 seq;
 	unsigned char	*sa, *p;
@@ -2888,9 +2888,9 @@ static unsigned int OnAuth(struct adapter *padapter,
 
 	issue_auth(padapter, pstat, (unsigned short)status);
 
-#endif /* CONFIG_88EU_AP_MODE */
 	return _FAIL;
 }
+#endif /* CONFIG_88EU_AP_MODE */
 
 static unsigned int OnAuthClient(struct adapter *padapter,
 				 struct recv_frame *precv_frame)