mm: use zone_is_initialized() instead of if(zone->wait_table)

Use "zone_is_initialized()" instead of "if (zone->wait_table)".
Simplify the code, no functional change.
Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -194,7 +194,7 @@ void register_page_bootmem_info_node(struct pglist_data *pgdat)
 
 	zone = &pgdat->node_zones[0];
 	for (; zone < pgdat->node_zones + MAX_NR_ZONES - 1; zone++) {
-		if (zone->wait_table) {
+		if (zone_is_initialized(zone)) {
 			nr_pages = zone->wait_table_hash_nr_entries
 				* sizeof(wait_queue_head_t);
 			nr_pages = PAGE_ALIGN(nr_pages) >> PAGE_SHIFT;