get M81 working

Marlin/Marlin.pde

@@ -938,14 +938,13 @@ FORCE_INLINE void process_commands()
       
       case 81: // M81 - ATX Power Off
       
-      #if (SUICIDE_PIN >-1)
+      #if defined SUICIDE_PIN && SUICIDE_PIN > -1
         st_synchronize();
         suicide();
-      #else
+      #elif (PS_ON_PIN > -1)
-        #if (PS_ON_PIN > -1) 
         SET_INPUT(PS_ON_PIN); //Floating
       #endif
-      #endif
+		break;
         
     case 82:
       axis_relative_modes[3] = false;