md: fix kabi broken in struct mddev

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6OMCC
CVE: NA

--------------------------------

Struct mddev is just used inside raid, just in case that md_mod is compiled
from new kernel, and raid1/raid10 or other out-of-tree raid are compiled
from old kernel.
Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-by: NHou Tao <houtao1@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>

drivers/md/md.h

@@ -530,9 +530,9 @@ struct mddev {
 	bool	serialize_policy:1;
 
 	/* Used to synchronize idle and frozen for action_store() */
-	struct mutex sync_mutex;
+	KABI_EXTEND(struct mutex sync_mutex)
 	/* The sequence number for sync thread */
-	atomic_t sync_seq;
+	KABI_EXTEND(atomic_t sync_seq)
 };
 
 enum recovery_flags {