md: fix kabi broken in struct mddev

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6T6VY
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: NYongqiang Liu <liuyongqiang13@huawei.com>

drivers/md/md.h

@@ -510,10 +510,12 @@ struct mddev {
 
 	bool	has_superblocks:1;
 
+#ifndef __GENKSYMS__
 	/* Used to synchronize idle and frozen for action_store() */
 	struct mutex sync_mutex;
 	/* The sequence number for sync thread */
 	atomic_t sync_seq;
+#endif
 };
 
 enum recovery_flags {