mempool:when deinit mempool,need mark dict NULL before free

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

mm/mempool/mempool_multiple.c

@@ -303,7 +303,7 @@ mempool_multiple_get_dict(FAR struct mempool_multiple_s *mpool,
   size_t row;
   size_t col;
 
-  if (mpool == NULL || blk == NULL)
+  if (mpool == NULL || blk == NULL || mpool->dict == NULL)
     {
       return NULL;
     }
@@ -888,6 +888,7 @@ void mempool_multiple_deinit(FAR struct mempool_multiple_s *mpool)
     }
 
   mempool_multiple_free_chunk(mpool, mpool->dict);
+  mpool->dict = NULL;
   nxrmutex_destroy(&mpool->lock);
   mpool->free(mpool->arg, mpool);
 }