Use uint8_t in EEPROM code

Marlin/src/HAL/HAL_AVR/persistent_store_eeprom.cpp

@@ -53,7 +53,7 @@ bool PersistentStore::write_data(int &pos, const uint8_t *value, size_t size, ui
 
 bool PersistentStore::read_data(int &pos, uint8_t* value, size_t size, uint16_t *crc, const bool writing/*=true*/) {
   do {
-    uint8_t c = eeprom_read_byte((unsigned char*)pos);
+    uint8_t c = eeprom_read_byte((uint8_t*)pos);
     if (writing) *value = c;
     crc16(crc, &c, 1);
     pos++;