typo fixed

Firmware/Marlin_main.cpp

@@ -6945,7 +6945,7 @@ void FlushSerialRequestResend()
 void ClearToSend()
 {
     previous_millis_cmd = millis();
-    if ((CMDBUFFER_CURRENT_TYPE == CMDBUFFER_CURRENT_TYPE_USB) || (CMDBUFFER_CURRENT_TYPE == CMDBUFFER_CURRENT_TYPE_USB))
+    if ((CMDBUFFER_CURRENT_TYPE == CMDBUFFER_CURRENT_TYPE_USB) || (CMDBUFFER_CURRENT_TYPE == CMDBUFFER_CURRENT_TYPE_USB_WITH_LINENR))
         SERIAL_PROTOCOLLNRPGM(_T(MSG_OK));
 }