Fix RGB Matrix using RGBW WS2812 LEDs (#9705)

This should be a pointer, as that is what the function expects.

quantum/rgb_matrix_drivers.c

@@ -128,7 +128,7 @@ static inline void setled(int i, uint8_t r, uint8_t g, uint8_t b) {
     rgb_matrix_ws2812_array[i].g = g;
     rgb_matrix_ws2812_array[i].b = b;
 #    ifdef RGBW
-    convert_rgb_to_rgbw(rgb_matrix_ws2812_array[i]);
+    convert_rgb_to_rgbw(&rgb_matrix_ws2812_array[i]);
 #    endif
 }