CBRK_BUZZER: allow to disable startup sound

The 'if [ $LOG_FILE = /dev/null ]' block can be removed, because
STARTUP_TUNE is already set in that case.

src/lib/circuit_breaker/circuit_breaker_params.c

@@ -154,7 +154,8 @@ PARAM_DEFINE_INT32(CBRK_GPSFAIL, 0);
  *
  * Setting this parameter to 782097 will disable the buzzer audio notification.
  *
- * WARNING: ENABLING THIS CIRCUIT BREAKER IS AT OWN RISK
+ * Setting this parameter to 782090 will disable the startup tune, while keeping
+ * all others enabled.
  *
  * @reboot_required true
  * @min 0