Fix lcd_preheat dummy variable types

Marlin/src/module/configuration_store.cpp

     _FIELD_TEST(lcd_preheat_hotend_temp);
 
     #if DISABLED(ULTIPANEL)
-      constexpr int lcd_preheat_hotend_temp[2] = { PREHEAT_1_TEMP_HOTEND, PREHEAT_2_TEMP_HOTEND },
-                    lcd_preheat_bed_temp[2] = { PREHEAT_1_TEMP_BED, PREHEAT_2_TEMP_BED },
-                    lcd_preheat_fan_speed[2] = { PREHEAT_1_FAN_SPEED, PREHEAT_2_FAN_SPEED };
+      constexpr int16_t lcd_preheat_hotend_temp[2] = { PREHEAT_1_TEMP_HOTEND, PREHEAT_2_TEMP_HOTEND },
+                        lcd_preheat_bed_temp[2] = { PREHEAT_1_TEMP_BED, PREHEAT_2_TEMP_BED },
+                        lcd_preheat_fan_speed[2] = { PREHEAT_1_FAN_SPEED, PREHEAT_2_FAN_SPEED };
     #endif
 
     EEPROM_WRITE(lcd_preheat_hotend_temp);
       _FIELD_TEST(lcd_preheat_hotend_temp);
 
       #if DISABLED(ULTIPANEL)
-        int lcd_preheat_hotend_temp[2], lcd_preheat_bed_temp[2], lcd_preheat_fan_speed[2];
+        int16_t lcd_preheat_hotend_temp[2], lcd_preheat_bed_temp[2], lcd_preheat_fan_speed[2];
       #endif
       EEPROM_READ(lcd_preheat_hotend_temp); // 2 floats
       EEPROM_READ(lcd_preheat_bed_temp);    // 2 floats