Revert errant const

Marlin/src/HAL/HAL_DUE/persistent_store_eeprom.cpp

Marlin/src/HAL/HAL_ESP32/persistent_store_spiffs.cpp

Marlin/src/HAL/HAL_LPC1768/persistent_store_flash.cpp

Marlin/src/HAL/HAL_SAMD51/persistent_store_eeprom.cpp

Marlin/src/HAL/HAL_STM32/persistent_store_impl.cpp

Marlin/src/HAL/HAL_STM32F1/persistent_store_eeprom.cpp

Marlin/src/HAL/HAL_STM32_F4_F7/persistent_store_eeprom.cpp

Marlin/src/HAL/HAL_TEENSY31_32/persistent_store_impl.cpp

Marlin/src/HAL/HAL_TEENSY35_36/persistent_store_eeprom.cpp

Marlin/src/HAL/shared/persistent_store_api.h