asterisk: use return in init script

"start_service()" is a function, hence "return" should be used instead
of "exit".

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

net/asterisk/files/asterisk.init

@@ -26,7 +26,7 @@ start_service() {
   config_get_bool enabled general enabled 0
   if [ $enabled -eq 0 ]; then
     $LOGGER service not enabled in /etc/config/$NAME
-    exit 1
+    return 1
   fi
 
   config_get_bool log_stderr general log_stderr 1