Fix RGBW for WS2812 SPI driver (#24367)

platforms/chibios/drivers/ws2812_spi.c

@@ -133,7 +133,7 @@ static void set_led_color_rgb(rgb_led_t color, int pos) {
 #endif
 #ifdef WS2812_RGBW
     for (int j = 0; j < 4; j++)
-        tx_start[BYTES_FOR_LED * pos + BYTES_FOR_LED_BYTE * 4 + j] = get_protocol_eq(color.w, j);
+        tx_start[BYTES_FOR_LED * pos + BYTES_FOR_LED_BYTE * 3 + j] = get_protocol_eq(color.w, j);
 #endif
 }