Fix missing LCD_STR_REFRESH

Marlin/Conditionals_LCD.h

     #define LCD_DEGREE_CHAR      0x01
     #define LCD_STR_THERMOMETER "\x02" // Still used with string concatenation
     #define LCD_UPLEVEL_CHAR     0x03
-    #define LCD_REFRESH_CHAR     0x04
+    #define LCD_STR_REFRESH     "\x04"
     #define LCD_STR_FOLDER      "\x05"
     #define LCD_FEEDRATE_CHAR    0x06
     #define LCD_CLOCK_CHAR       0x07

Marlin/ultralcd_impl_HD44780.h

         }
         else { // Custom characters for submenus
           createChar_P(LCD_UPLEVEL_CHAR, uplevel);
-          createChar_P(LCD_REFRESH_CHAR, refresh);
+          createChar_P(LCD_STR_REFRESH[0], refresh);
           createChar_P(LCD_STR_FOLDER[0], folder);
         }
       }
     #else
       createChar_P(LCD_UPLEVEL_CHAR, uplevel);
-      createChar_P(LCD_REFRESH_CHAR, refresh);
+      createChar_P(LCD_STR_REFRESH[0], refresh);
       createChar_P(LCD_STR_FOLDER[0], folder);
     #endif