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/raid1.c b/drivers/md/raid1.c
index e09f595..e023a25 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2738,7 +2738,7 @@
 	return ERR_PTR(-EINVAL);
 }
 
-static struct mdk_personality raid1_personality =
+static struct md_personality raid1_personality =
 {
 	.name		= "raid1",
 	.level		= 1,