FreeTDM: Silence -Wtautological-compare warnings emitted by clang

Fixes "warning: comparison of unsigned expression >= 0 is always true".
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>

libs/freetdm/src/ftmod/ftmod_analog/ftmod_analog.c

@@ -222,10 +222,7 @@ static FIO_SIG_CONFIGURE_FUNCTION(ftdm_analog_configure_span)
 			if (!(intval = va_arg(ap, int *))) {
 				break;
 			}
-			wait_dialtone_timeout = *intval;
-			if (wait_dialtone_timeout < 0) {
-				wait_dialtone_timeout = 0;
-			}
+			wait_dialtone_timeout = ftdm_max(0, *intval);
 			ftdm_log(FTDM_LOG_DEBUG, "Wait dial tone ms = %d\n", wait_dialtone_timeout);
 		} else if (!strcasecmp(var, "enable_callerid")) {
 			if (!(val = va_arg(ap, char *))) {

libs/freetdm/src/ftmod/ftmod_libpri/lpwrap_pri.c

@@ -61,7 +61,7 @@ static struct lpwrap_pri_event_list LPWRAP_PRI_EVENT_LIST[LPWRAP_PRI_EVENT_MAX]
 
 const char *lpwrap_pri_event_str(lpwrap_pri_event_t event_id)
 {
-	if (event_id < 0 || event_id >= LPWRAP_PRI_EVENT_MAX)
+	if (event_id >= LPWRAP_PRI_EVENT_MAX)
 		return "";
 
 	return LPWRAP_PRI_EVENT_LIST[event_id].name;

libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c

@@ -665,7 +665,7 @@ static FIO_OPEN_FUNCTION(zt_open)
 			}
 		}
 
-		if (zt_globals.eclevel >= 0) {
+		if (1) {
 			int len = zt_globals.eclevel;
 			if (len) {
 				ftdm_log(FTDM_LOG_INFO, "Setting echo cancel to %d taps for %d:%d\n", len, ftdmchan->span_id, ftdmchan->chan_id);