Fix low contrast on Minipanel display (#17601)

Marlin/src/inc/Conditionals_post.h

@@ -289,8 +289,10 @@
 #elif ENABLED(ULTI_CONTROLLER)
   #define _LCD_CONTRAST_INIT 127
   #define _LCD_CONTRAST_MAX  254
-#elif EITHER(MAKRPANEL, MINIPANEL)
+#elif ENABLED(MAKRPANEL)
   #define _LCD_CONTRAST_INIT  17
+#elif ENABLED(MINIPANEL)
+  #define _LCD_CONTRAST_INIT  150
 #endif
 
 #ifdef _LCD_CONTRAST_INIT