Fix ST7920 timing for Rumba32, Fysetc S6 (#20556)

Marlin/src/pins/stm32f4/pins_FYSETC_S6.h

@@ -273,7 +273,7 @@
       #define BOARD_ST7920_DELAY_2  DELAY_NS(48)
     #endif
     #ifndef BOARD_ST7920_DELAY_3
-      #define BOARD_ST7920_DELAY_3 DELAY_NS(600)
+      #define BOARD_ST7920_DELAY_3 DELAY_NS(640)
     #endif
   #endif
 

Marlin/src/pins/stm32f4/pins_RUMBA32_common.h

@@ -180,7 +180,7 @@
       #define BOARD_ST7920_DELAY_2 DELAY_NS(48)
     #endif
     #ifndef BOARD_ST7920_DELAY_3
-      #define BOARD_ST7920_DELAY_3 DELAY_NS(600)
+      #define BOARD_ST7920_DELAY_3 DELAY_NS(640)
     #endif
   #endif