md: rename "mdk_personality" to "md_personality"

"mdk" doesn't mean anything any more.

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index f6a9b0c..8427ff1 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -3050,7 +3050,7 @@
 	return ERR_PTR(-EINVAL);
 }
 
-static struct mdk_personality raid10_personality =
+static struct md_personality raid10_personality =
 {
 	.name		= "raid10",
 	.level		= 10,