md: remove unused static md_wq workqueue

The md_wq workqueue is defined as static and initialized in md_init(),
but it is not used anywhere within md.c.

All asynchronous and deferred work in this file is handled via
md_misc_wq or dedicated md threads.

Fixes: b75197e ("md: Remove flush handling")
Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
Link: https://lore.kernel.org/linux-raid/20260328193522.3624-1-abd.masalkhi@gmail.com/
Signed-off-by: Yu Kuai <yukuai@fnnas.com>

Author: masalkhi

drivers/md/md.c

@@ -84,7 +84,6 @@ static DEFINE_XARRAY(md_submodule);
 static const struct kobj_type md_ktype;
 
 static DECLARE_WAIT_QUEUE_HEAD(resync_wait);
-static struct workqueue_struct *md_wq;
 
 /*
  * This workqueue is used for sync_work to register new sync_thread, and for
@@ -10511,10 +10510,6 @@ static int __init md_init(void)
 		goto err_bitmap;
 
 	ret = -ENOMEM;
-	md_wq = alloc_workqueue("md", WQ_MEM_RECLAIM | WQ_PERCPU, 0);
-	if (!md_wq)
-		goto err_wq;
-
 	md_misc_wq = alloc_workqueue("md_misc", WQ_PERCPU, 0);
 	if (!md_misc_wq)
 		goto err_misc_wq;
@@ -10539,8 +10534,6 @@ static int __init md_init(void)
 err_md:
 	destroy_workqueue(md_misc_wq);
 err_misc_wq:
-	destroy_workqueue(md_wq);
-err_wq:
 	md_llbitmap_exit();
 err_bitmap:
 	md_bitmap_exit();
@@ -10849,7 +10842,6 @@ static __exit void md_exit(void)
 	spin_unlock(&all_mddevs_lock);
 
 	destroy_workqueue(md_misc_wq);
-	destroy_workqueue(md_wq);
 	md_bitmap_exit();
 }