Fix sporadic compile error

Sometimes the compiler can't figure out that a pointer is never used
unitialized, so we help it out.

quantum/process_keycode/process_combo.c

@@ -971,7 +971,7 @@ void reset_combos(void) {
     ripe_head = active_head = COMBO_NULL_STATE;
 
     inactive_head = 0;
-    combo_t *combo;
+    combo_t *combo = &key_combos[0];
     for (combo_state_t i = 0; i < COMBO_LEN; i++) {
         combo = &key_combos[i];
         SET_NEXT_COMBO(combo, (i + 1));