Contrast over 63 assume 255 max

This is closer to the prior behavior.

Marlin/src/inc/Conditionals_post.h

     #ifdef _LCD_CONTRAST_MAX
       #define LCD_CONTRAST_MAX _LCD_CONTRAST_MAX
     #elif _LCD_CONTRAST_INIT > 63
-      #define LCD_CONTRAST_MAX _LCD_CONTRAST_INIT
+      #define LCD_CONTRAST_MAX 255
     #else
       #define LCD_CONTRAST_MAX 63   // ST7567 6-bits contrast
     #endif