Remove use of __flash due to LTO issues (#15268)

docs/feature_led_matrix.md

@@ -54,7 +54,7 @@ For split keyboards using `LED_MATRIX_SPLIT` with an LED driver, you can either
 Define these arrays listing all the LEDs in your `<keyboard>.c`:
 
 ```c
-const is31_led __flash g_is31_leds[DRIVER_LED_TOTAL] = {
+const is31_led PROGMEM g_is31_leds[DRIVER_LED_TOTAL] = {
 /* Refer to IS31 manual for these locations
  *    driver
  *    |  LED address