config: utilize devmode variable

This holds the NX hw state.

bootloader/main.c

@@ -1182,7 +1182,7 @@ static void _show_errors()
 
 static void _check_low_battery()
 {
-	if (fuse_read_hw_state() == FUSE_NX_HW_STATE_DEV)
+	if (h_cfg.devmode)
 		goto out;
 
 	int enough_battery;