memory tier: use helper function destroy_memory_type()

Use helper function destroy_memory_type() to release memtype instead of
open code it to help improve code readability a bit.  No functional change
intended.

Link: https://lkml.kernel.org/r/20230626121053.1916447-1-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Wei Xu <weixugc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory-tiers.c

@@ -586,7 +586,7 @@ void clear_node_memory_type(int node, struct memory_dev_type *memtype)
 	 */
 	if (!node_memory_types[node].map_count) {
 		node_memory_types[node].memtype = NULL;
-		kref_put(&memtype->kref, release_memtype);
+		destroy_memory_type(memtype);
 	}
 	mutex_unlock(&memory_tier_lock);
 }