LCD_UBL_memory_slot_corrections (#7516)

* LCD_UBL_memory_slot_corrections

Changed the memory slot edit function to work with the
`settings.calc_num_meshes()`

* Add a little more safety margin...

* More corrections

Error handling when the EEPROM is not available.

Marlin/src/HAL/HAL_LPC1768/HAL.cpp

@@ -127,7 +127,6 @@ void HAL_adc_start_conversion(uint8_t adc_pin) {
 }
 
 bool HAL_adc_finished(void) {
-  uint32_t data = LPC_ADC->ADGDR;
   return LPC_ADC->ADGDR & ADC_DONE;
 }