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/linear.c b/drivers/md/linear.c
index cbac48c..10c5844 100644
--- a/drivers/md/linear.c
+++ b/drivers/md/linear.c
@@ -330,7 +330,7 @@
 }
 
 
-static struct mdk_personality linear_personality =
+static struct md_personality linear_personality =
 {
 	.name		= "linear",
 	.level		= LEVEL_LINEAR,