MDEV-21212 fixup: GCC -Wclass-memaccess

storage/innobase/buf/buf0buf.cc

@@ -3897,8 +3897,8 @@ void buf_pool_invalidate()
 	buf_pool.freed_page_clock = 0;
 	buf_pool.LRU_old = NULL;
 	buf_pool.LRU_old_len = 0;
+	buf_pool.stat.init();
 
-	memset(&buf_pool.stat, 0x00, sizeof(buf_pool.stat));
 	buf_refresh_io_stats();
 	mysql_mutex_unlock(&buf_pool.mutex);
 }

storage/innobase/include/buf0buf.h

@@ -1220,6 +1220,9 @@ struct buf_buddy_free_t {
 
 /** @brief The buffer pool statistics structure. */
 struct buf_pool_stat_t{
+	/** Initialize the counters */
+	void init() { memset((void*) this, 0, sizeof *this); }
+
 	ib_counter_t<ulint>	n_page_gets;
 				/*!< number of page gets performed;
 				also successful searches through