Optimize menu selection for Viki rotary encoder.

The Viki LCD rotary encoder uses a different number of steps per
rotation. This fixes the seeming "missed" steps when selecting a menu.

Marlin/ultralcd.cpp

 static void menu_action_setting_edit_callback_float52(const char* pstr, float* ptr, float minValue, float maxValue, menuFunc_t callbackFunc);
 static void menu_action_setting_edit_callback_long5(const char* pstr, unsigned long* ptr, unsigned long minValue, unsigned long maxValue, menuFunc_t callbackFunc);
 
-#define ENCODER_STEPS_PER_MENU_ITEM 5
+#if !defined(LCD_I2C_VIKI)
+  #define ENCODER_STEPS_PER_MENU_ITEM 5
+#else
+  #define ENCODER_STEPS_PER_MENU_ITEM 2 // VIKI LCD rotary encoder uses a different number of steps per rotation
+#endif
 
 /* Helper macros for menus */
 #define START_MENU() do { \