Fix KILL_PIN assignment for MKS_MINI_12864

According to #13397

Marlin/src/pins/pins_RAMPS.h

       #define BTN_ENC           35
 
       #define SD_DETECT_PIN     49
-      #define KILL_PIN          64
+      #define KILL_PIN          41
 
     #elif ENABLED(MINIPANEL)