Update POWER_LOSS_PIN comment (#16957)

Marlin/Configuration_adv.h

@@ -1044,7 +1044,7 @@
   #if ENABLED(POWER_LOSS_RECOVERY)
     //#define BACKUP_POWER_SUPPLY       // Backup power / UPS to move the steppers on power loss
     //#define POWER_LOSS_ZRAISE       2 // (mm) Z axis raise on resume (on power loss with UPS)
-    //#define POWER_LOSS_PIN         44 // Pin to detect power loss
+    //#define POWER_LOSS_PIN         44 // Pin to detect power loss. Set to -1 to disable default pin on boards without module.
     //#define POWER_LOSS_STATE     HIGH // State of pin indicating power loss
     //#define POWER_LOSS_PULL           // Set pullup / pulldown as appropriate
     //#define POWER_LOSS_PURGE_LEN   20 // (mm) Length of filament to purge on resume