patch 8.1.1465: allocating wrong amount of memory

Problem:    Allocating wrong amount of memory. (Yegappan Lakshmanan)
Solution:   Use sizeof() for right type of struct.
diff --git a/src/memfile_test.c b/src/memfile_test.c
index 8408498..0a20330 100644
--- a/src/memfile_test.c
+++ b/src/memfile_test.c
@@ -67,7 +67,7 @@
 	assert(mf_hash_find(&ht, key) == NULL);
 
 	/* allocate and add new item */
-	item = LALLOC_CLEAR_ONE(mf_hashtab_T);
+	item = LALLOC_CLEAR_ONE(mf_hashitem_T);
 	assert(item != NULL);
 	item->mhi_key = key;
 	mf_hash_add_item(&ht, item);