[2.0.x] Fix compile errors (#9141)

* Update persistent_store_impl.cpp
* Remove define BYTE from serial functions since Arduino docs typically show 0 for the normal case.

Marlin/src/module/configuration_store.h

@@ -116,7 +116,7 @@ class MarlinSettings {
       );
       static bool size_error(const uint16_t size
         #if ADD_PORT_ARG
-          const int8_t port=-1
+          , const int8_t port=-1
         #endif
       );
     #endif