md: Improve name of threads created by md_register_thread

The management thread for raid4,5,6 arrays are all called
mdX_raid5, independent of the actual raid level, which is wrong and
can be confusion.

So change md_register_thread to use the name from the personality
unless no alternate name (like 'resync' or 'reshape') is given.

This is simpler and more correct.

Cc: Jinzc <zhenchengjin@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 8bca383..7872968 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2188,7 +2188,7 @@
 	}
 
 
-	mddev->thread = md_register_thread(raid10d, mddev, "%s_raid10");
+	mddev->thread = md_register_thread(raid10d, mddev, NULL);
 	if (!mddev->thread) {
 		printk(KERN_ERR
 		       "raid10: couldn't allocate thread for %s\n",