Use serial macro in sd_mmc_spi_mem.cpp for Due

Marlin/src/HAL/HAL_DUE/usb/sd_mmc_spi_mem.cpp

   #ifdef DEBUG_MMC
     char buffer[80];
     sprintf(buffer, "SDRD: %d @ 0x%08x\n", nb_sector, addr);
-    MYSERIAL0.print(buffer);
+    SERIAL_PROTOCOL_P(0, buffer);
   #endif
 
   // Start reading
   #ifdef DEBUG_MMC
     char buffer[80];
     sprintf(buffer, "SDWR: %d @ 0x%08x\n", nb_sector, addr);
-    MYSERIAL0.print(buffer);
+    SERIAL_PROTOCOL_P(0, buffer);
   #endif
 
   if (!card.getSd2Card().writeStart(addr, nb_sector))