Use more consistent iface->conf checks

Commit f1df4fbfc7 ("mesh: Use setup completion callback to complete
mesh join") added a check for iface->conf being NULL into a debug print.
However, it is not clear how that could be NULL here. In any case,
setup_interface() could end up dereferencing iface->conf in the call to
hostapd_validate_bssid_configuration(), so better be consistent with the
checks and not get warnings from static analyzers regardless of whether
this can happen in practice.

Signed-off-by: Jouni Malinen <j@w1.fi>

src/ap/hostapd.c

@@ -2308,10 +2308,12 @@ int hostapd_setup_interface(struct hostapd_iface *iface)
 {
 	int ret;
 
+	if (!iface->conf)
+		return -1;
 	ret = setup_interface(iface);
 	if (ret) {
 		wpa_printf(MSG_ERROR, "%s: Unable to setup interface.",
-			   iface->conf ? iface->conf->bss[0]->iface : "N/A");
+			   iface->conf->bss[0]->iface);
 		return -1;
 	}