Change `led` variable in rgb_matrix_drivers to avoid conflicts (#9412)

* Change `led` to `led_matrix` in rgb_matrix_drivers

Is a minor change that only affects the driver file. 

However, this will allow somebody to run rgblight along side rgb matrix
using the ws2812 driver, as well.  Specifically, so you can use the
custom driver for rgblight to set a different pin (barring a change to
the `ws2812_setleds` function).  

Courtesy of discord conversion:
https://discordapp.com/channels/440868230475677696/568161140534935572/721555623191248906

* Change name to be super specific

* Update rgb_matrix_drivers.c

quantum/rgb_matrix_drivers.c

@@ -115,27 +115,27 @@ const rgb_matrix_driver_t rgb_matrix_driver = {
 #elif defined(WS2812)
 
 // LED color buffer
-LED_TYPE led[DRIVER_LED_TOTAL];
+LED_TYPE rgb_matrix_ws2812_array[DRIVER_LED_TOTAL];
 
 static void init(void) {}
 
 static void flush(void) {
     // Assumes use of RGB_DI_PIN
-    ws2812_setleds(led, DRIVER_LED_TOTAL);
+    ws2812_setleds(rgb_matrix_ws2812_array, DRIVER_LED_TOTAL);
 }
 
 // Set an led in the buffer to a color
 static inline void setled(int i, uint8_t r, uint8_t g, uint8_t b) {
-    led[i].r = r;
-    led[i].g = g;
-    led[i].b = b;
+    rgb_matrix_ws2812_array[i].r = r;
+    rgb_matrix_ws2812_array[i].g = g;
+    rgb_matrix_ws2812_array[i].b = b;
 #    ifdef RGBW
-    convert_rgb_to_rgbw(led[i]);
+    convert_rgb_to_rgbw(rgb_matrix_ws2812_array[i]);
 #    endif
 }
 
 static void setled_all(uint8_t r, uint8_t g, uint8_t b) {
-    for (int i = 0; i < sizeof(led) / sizeof(led[0]); i++) {
+    for (int i = 0; i < sizeof(rgb_matrix_ws2812_array) / sizeof(rgb_matrix_ws2812_array[0]); i++) {
         setled(i, r, g, b);
     }
 }