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/faulty.c b/drivers/md/faulty.c
index 571445e..60816b1 100644
--- a/drivers/md/faulty.c
+++ b/drivers/md/faulty.c
@@ -334,7 +334,7 @@
 	return 0;
 }
 
-static struct mdk_personality faulty_personality =
+static struct md_personality faulty_personality =
 {
 	.name		= "faulty",
 	.level		= LEVEL_FAULTY,