Reduce AVR clock to 8MHz

tmk_core/protocol/lufa/lufa.c

@@ -917,8 +917,14 @@ static void setup_mcu(void) {
     MCUSR &= ~_BV(WDRF);
     wdt_disable();
 
+// HACK for System76 boards with AVR at 3.3V and crystal at 16 MHz
+#if (F_CPU == 8000000 && F_USB == 16000000)
+    /* Divide clock by 2 */
+    clock_prescale_set(clock_div_2);
+#else
     /* Disable clock division */
     clock_prescale_set(clock_div_1);
+#endif
 }
 
 /** \brief Setup USB