spinlock: use spin_lock_init replace spin_initialize

reason:
1: spin_lock_init and spin_initialize have similar functionalities.
2: spin_lock and spin_unlock should be called in matching pairs.

Signed-off-by: hujun5 <hujun5@xiaomi.com>

mm/mempool/mempool.c

@@ -304,7 +304,7 @@ int mempool_init(FAR struct mempool_s *pool, FAR const char *name)
       kasan_poison(base, size);
     }
 
-  spin_initialize(&pool->lock, SP_UNLOCKED);
+  spin_lock_init(&pool->lock);
   if (pool->wait && pool->expandsize == 0)
     {
       nxsem_init(&pool->waitsem, 0, 0);