Define RGB_DI_PIN directly instead of using another define (#20983)

keyboards/keebio/cepstrum/rev1/config.h

@@ -57,7 +57,7 @@
 #define RGB_MATRIX_MAXIMUM_BRIGHTNESS 120
 #define RGB_MATRIX_DEFAULT_VAL RGB_MATRIX_MAXIMUM_BRIGHTNESS
 #define WS2812_DI_PIN GP18
-#define RGB_DI_PIN WS2812_DI_PIN
+#define RGB_DI_PIN GP18
 #define RGB_MATRIX_LED_COUNT 96
 #define RGB_DISABLE_WHEN_USB_SUSPENDED
 #define RGB_MATRIX_FRAMEBUFFER_EFFECTS