P2P: Suppress warning on non-P2P config

Without CONFIG_P2P config, the following warning occurs if CONFIG_AP is
enabled for the build:

ap.c: In function ‘wpas_conf_ap_vht’:
ap.c:54:5: warning: unused variable ‘channel’ [-Wunused-variable]
  u8 channel = conf->channel;
     ^
ap.c:53:5: warning: unused variable ‘center_chan’ [-Wunused-variable]
  u8 center_chan = 0;
     ^

Signed-off-by: Masashi Honma <masashi.honma@gmail.com>

wpa_supplicant/ap.c

@@ -50,8 +50,10 @@ static void wpas_conf_ap_vht(struct wpa_supplicant *wpa_s,
 			     struct hostapd_config *conf,
 			     struct hostapd_hw_modes *mode)
 {
+#ifdef CONFIG_P2P
 	u8 center_chan = 0;
 	u8 channel = conf->channel;
+#endif /* CONFIG_P2P */
 
 	if (!conf->secondary_channel)
 		goto no_vht;