Use SERIAL_EOL in SERIAL_PROTOCOLLN macros

Marlin/Marlin.h

 #define SERIAL_PROTOCOL(x) MYSERIAL.print(x)
 #define SERIAL_PROTOCOL_F(x,y) MYSERIAL.print(x,y)
 #define SERIAL_PROTOCOLPGM(x) serialprintPGM(PSTR(x))
-#define SERIAL_PROTOCOLLN(x) do{ MYSERIAL.print(x),MYSERIAL.write('\n'); }while(0)
-#define SERIAL_PROTOCOLLNPGM(x) do{ serialprintPGM(PSTR(x)),MYSERIAL.write('\n'); }while(0)
+#define SERIAL_PROTOCOLLN(x) do{ MYSERIAL.print(x); SERIAL_EOL; }while(0)
+#define SERIAL_PROTOCOLLNPGM(x) do{ serialprintPGM(PSTR(x)); SERIAL_EOL; }while(0)
 
 
 extern const char errormagic[] PROGMEM;